My understanding is if you spend more than 183 days in the USA in a 12 month period , the IRS wants you to pay taxes on ALL of your income.
So you would pay Canadian taxes and US taxes.
Note that it is 183 days so they don't have to be consecutive.
Hopefully someone with more experience will chime in.
2014 Chevrolet 3500 CC 4X4 Duramax, Tork Lift Tiedowns, TorkLift Fastguns, Superhitch and supertruss
2009 Jayco 213 SOLD
2008 Bigfoot 25C9.4