The best solution I’ve used, and recommended to others, is Google Fi. It uses the T-Mobile network in the US mostly, and roams on several Canadian providers. I’ve used the Unlimited Plus plan which was just upgraded to 50GB of data a month, and that includes roaming too which is much higher than just about anything out there.
Just be careful about how many months you use it consecutively. I’ve heard of them canceling plans due to terms of service if you roam constantly. You also will be throttled or slowed down after the 50GB data amount, and that can be a red flag as well if you use all of your roaming data constantly.