Having a visa doesn't give you the right to enter. I don't think permanent residency does either.

It's always at the discretion of the immigration officer and there's no recourse if they don't let you in.

Personally, I don't think it's generally reasonable to jail at entry when denying entry is an option. The case where the UK tourist was denied entry to Canada from the US and then was jailed in the US is a case where denying entry isn't really possible, because if neither side of a land border will allow entry, what do uou do... but then it shouldn't have taken more than a couple days to make arrangements for her to fly home on her own dime.