Anyone got any experience or information on the legalities/procedures for assigning a tenancy agreement?

You need to obtain the landlords consent. You are also liable for the rent in the event the sub tenant doesn't pay.

Forms: http://www.lawdepot.ca/contracts/canada/Alberta/
Info: http://landlordandtenant.org/lldurin...ssignment.aspx

It's relatively straightforward by the nuances of what you can and what you cannot do will be governed by the tenancy agreement.

Section 22 of the Residential Tenancies Act sets of the legal framework for assignments. A copy of it is here: Residential Tenancies Act

...consent not to be unreasonably withheld.

As I understand it when an agreement is assigned that means the original tenant no longer has any liability to the landlord and all liability goes to the new tenant ie it is quite different to sub-letting where the original tenant is still liable to the landlord?

Tenant has to ask for consent of the landlord to assign. What would be reasonable grounds for the landlord to object to assignment?

Would it be advisable to use a lawyer for the legal agreement to assign? Does the landlord sign the assignment agreement or is it just the original and new tenant?

I've recently moved into a new rented house. Unfortunately there was very little choice just at the time we had to move so if the opportunity arises to move I just want to understand what we would be entitled to do.

That will depend upon the terms of the assignment.

How much time have you got? There is nothing particularly technical about it. If two people discussing it would believe it is unreasonable, it likely is. The landlord may not want: a tenant that is a smoker; a tenant that works strange hours and may affect other tenants when coming and going; a tenant with pets; a tenant with a history of non payment of rent, etc.

That is a judgement call for you to make. The landlord may not sign and, if not, just the other two will sign. If I was drafting it, I would want the landlord to sign it, to provide evidence of his/her consent.

As a landlord, I would not absolve the original tenant from liability. I would allow reassignment, however only with the caveat that should the assignee default, the original tenant remained responsible for unpaid rent and any damages without the need for me to go to court and seek redress from the assignee. I would never enter into such an agreement without legal advice.