A bit of a strange request...

I'm still in the UK, but want to receive texts on a Canadian mobile number from here. This poses a number of issues:
1) I need roaming
2) I need to get the sim here
3) It needs to be activated

Is such a thing possible?

Thanks in advance.

Will this work?

https://uk.simcorner.com/collections/canada-sim-card

Oh interesting. Thanks - checking now.
Can they tell it's a US and not Candian number?

Yes different cities and provinces in Canada have different area codes. For example BC is 604 and 250, as well as 778 and 236 commonly used in Vancouver. So people can tell where the number is coming from based on that (e.g. 604 555 1234 is a BC number).

Unless the # is being spoofed as in the cases of hoax calls in India purporting to be from the CRA and these numbers are showing 613 area codes which is Ottawa.

You could get virtual SMS just for communicating - but why do you specifically need a Canada number to do so? If it's to imply that you are in Canada when you are not (for example, for job application or a rental application purpose) I would recommend you don't do so. You could be called to interview/meet/view at few days notice - with the present situation, you may not be able to get consent to fly quickly.

https://smsreceivefree.com/
https://getfreesmsnumber.com/

(lots of others available)

I'm getting spoof calls beginning with 604!

Let alone lots of others with area codes imitating other Canadian and US numbes.

Oh, those are useful. Thanks.

I just needed it for KYC, but it turns out that ID and face scan are enough without the mobile number.

They can spoof any number; I got a scam call and dialed back, and it was a Sask provincial government office.