For several reasons, I'd like to partake in an MBA in Canada, at a top school, and only then move to the US, but I'd like to know whether the prospects there are good after acquiring an MBA in a top Canadian business school. Are these actually highly regarded in the US, or will I ever be "behind" any applicants from top US schools?

Because you wrote "move" rather than "return", you might not have the right to work in US. If so, studying a STEM-status MBA in the US would give you OPT allowing employers to hire you for two initial years easily. As a non-US resident with a non-US degree, you have minimal job opportunities in the US. 

PS So, whether or not the top Canadian schools are highly regarded is secondary. Generally, the top MBAs (at Queen's, Toronto and Western universities) serve the Ontario labour market. They are seen as being on a slightly lower level than, for example, the US schools in the FT top 100. That's reflected in the average salaries: even the highest Canadian school is well below the lowest US school's average salary. 

[Edited by Duncan on Jul 08, 2023]