My wife is a Yank and she files 2 returns - first in Canada and then in US. But she is a Canadian resident. After she pays Canadian taxes her American taxes owing are nothing. US taxes are a tiny fraction of Canadian taxes.
One of my sons is a dual citizen in hockey and lives/resides in Florida but used to play here in Canada most of his home games. His team deducted his tax withholding every 2 weeks from his pay. and then you have to deal with CRA to get back some tax withholdings as a US resident. Da teams have no say in this issue. And unless you have a great tax plan which expensive tax accountants prepare/defend for you you are not gonna fight them on your own. It is complex stuff like real complex. Guys like Matty would pay well north of $100K per on this expertise at like $1,800 per hour.