Is he a Canadian resident meaning he is PR or is he a citizen? If he is a citizen of Canada, he will have no problem sponsoring you for PR of Canada at any time no matter how long he stays in the US, regardless of him getting a green card or dual citizenship.
If he is a PR of Canada, he needs to be careful that he does not stay in the US too long or he will lose it. A PR of Canada can be outside Canada for up to 3 years out of every 5. In the meantime, if you have sponsored him for a US green card and he leaves the US to fulfil his PR obligations in Canada, he also risks losing his US green card again. That you can lose if you have left the US for more than a year, even in some cases less depending on the IO determination of if he has permanently left the US. If he is a PR of Canada, it would be better for him to get citizenship first before he goes to the US.
