Can someone do another Masters in Canada if you already have a Masters and PhD from the UK?

I know a lecturer in my university who did his Masters and PhD in Computer Science and also has a Masters in soil science. So yes, you could do any number of Masters you want. I doubt immigration really cares about your background. If you have admission and support letter from a Canadian university, you should be able to get a visa. And if you are paying fees for your Masters it is unlikely you will have any problems.

You can study for a second masters, but funding may have different conditions.

I know several people with 2 masters and their did them for their own reasons.