Roaming in Canada using a US carrier has always been hit or miss, but this last year it got worse than it has been the last few years. All of the providers have reduced the amount of roaming data you can use across just about all of their existing plans.
Google Fi and/or T-Mobile seem to be the best choice right now for roaming if you’re looking for a new plan, but there have been wildly different reports from users. I’ve been using both T-Mobile and Google Fi with good results, but some folks have reported very poor performance or being cut off early in their data amounts.
Generally speaking, and it seems like a lot of people have forgot about roaming (maybe because of not being in Canada during the pandemic), roaming is always a crap shoot, and usually only usable for emergencies. That hasn’t changed - if I were only able to use cellular in Canada, I would use it just for basic browsing and access, and would have to rely on local WiFi for any sort of streaming or remote work.