Quick Guide to Canadian Immigration
 Express Entry
This is a Federal program, whereby skilled applicants apply to enter a 'pool', and then CIC pick those with the highest points score on the Comprehensive Ranking System and invite them to apply for PR.
Once you are in the pool, to be in with a chance of being selected and receiving an invitation, you will need to score above approximately 450 as a rough guide. If you don't score enough, then you'll need to look at other visa routes and/or get a job offer and LMIA to boost your points score. Please note that the FSW Trades the points required are much lower.
If your company has offices in Canada, you may be able to get an intra-company transfer.
If you have at least 2 years self-employed experience out of the previous 5 years, in a qualifying occupation (cultural/athletic/farming) you can consider this program. [CIC website].
Canadian Experience Class (Now part of Express Entry but worth points and can be invited 'under it')
If you have worked full-time (or the equivalent in part time over a longer period) in Canada for at least 1 years in a Skilled job, or you have spent 2 years studying in Canada followed by a year's Skilled work experience, then you would qualify for Permanent Residency under this program. https://www.canada.ca/en/immigration-refugees-citizenship/services/immigrate-canada/express-entry/become-candidate/eligibility/canadian-experience-class.html
If you do not fall in to any other category for immigration, as outlined in this guide, then your only option is to try and find a job offer to get a visa.
If you find an employer who is willing to hire you, the employer can apply to get the job offer approved by the government to be able to hire you. This is in the form of an LMIA, or Labour Market Impact Assessment.
The LMIA route gets you into Canada as it can be used to apply for a Temporary Work Permit. To get the LMIA, your potential employer must pay $1000 and prove that they have advertised the job across Canada and been unable to find a Canadian willing, or able, to do the job.
However, your work permit will have an expiry date between 1 and 3 years after you land in Canada (at which point you will be required to leave unless you have obtained Permanent Residency, or if not, can get a new Temporary Work Permit), and you will only be permitted to work for that employer. Your Work Permit can sometimes be used to apply for Permanent Residence, depending on the Skill Level and province.¹. [HRSDC website].
Sometimes CIC allows certain types of jobs to be LMIA exempt, and there are various categories of workers that fall under this criteria, including intra-company transfers. []
Provincial Sponsorship / Nominee
However, most Provinces in Canada have what is known as Provincial Sponsorship or Provincial Nominee, which allows you to immigrate to Canada through the Province you are living in. The following provinces offer programmes that allow you to be sponsored in with a Work Permit in occupations at a lower skill level.
ALL Provincial Nominee Programs: https://www.canada.ca/en/immigration-refugees-citizenship/services/immigrate-canada/provincial-nominees/eligibility.html#websites
If you can secure a place at a university, college or technical institution, you can apply for a study permit [CIC Website]. This will allow you to study in Canada for the duration of your course. You can use two years of your study time to count towards Permanent Residence by applying under Canadian Experience Class [CIC Website], however an additional year of skilled work in Canada is also required (under a Work Permit).
 Family / Canadian Relatives
If your mother or father is Canadian, you may be able to claim Canadian Citizenship.
You may be able to get your Canadian spouse, adult child or grandchild to sponsor you, or possibly another family member (i.e. a sibling, aunt, cousin, etc) if they meet the fairly narrow criteria set out in the aforementioned link.
This varies from province to province, however in some provinces more distant relatives are able to sponsor you into Canada under a Provincial Nominee Program.
Terminated programs: Federal Immigrant Investor and Entrepreneurs, this program has been terminated. On June 19, 2014, applications still in the backlog of the federal Immigrant Investor Program and Entrepreneur Program were terminated.
Edited to add, there are various business investment programs still available for certain other Provinces. More details here: http://www.canadabusiness.ca/eng/page/2783/
There is also the "Start Up" program: http://www.cic.gc.ca/english/immigrate/business/start-up/index.asp
To be eligible for this program, you must:
Have, alone or with his accompanying spouse, including de facto spouse, net assets of at least $1,600,000 CAN obtained legally, excluding the amounts received by donation less than six months before the date on which the application was filed. Have experience in management in a legal farming, commercial or industrial business, or in a legal professional business where the staff, excluding the investor, occupies at least the equivalent of two full-time jobs, or for an international agency or a government or one of its departments or agencies;
We define management experience as the exercise, for at least two years in the five years preceding the application for a selection certificate, of duties related to the planning, management and control of financial resources and of human or material resources under your authority; the experience does not include experience acquired in the context of an apprenticeship, training or specialization process attested to by a diploma. Intend to settle in Québec and sign an agreement to invest $800,000 CAN with a financial intermediary (broker or trust company) authorized to participate in the Investor Program.
Quebec Entrepreneur Program http://tinyurl.com/4x3xw4o
Entrepreneur candidate Your experience as a entrepreneur, your ability to successfully carry out a business plan, your efforts to acquire a business in Québec, your assets and their lawful acquisition.
 Provincial Programs
Each province has their own Provincial Nominee Program, and each of these have many different streams. It is worth exploring them, especially as some of them are more 'open' than the Federal programs, so it is possible to get Permanent Residency without a job offer for example. []
 International Experience Canada
If you are a UK citizen between 18 and 30 (inclusive - or 18-35 if you are a citizen of the Republic of Ireland) you can enter Canada on a 24-month open visa through the IEC.
See the International Experience Canada article for more information.
See http://britishexpats.com/wiki/Implied_Status_IEC for more information