Since your spouse is in US on a working status (likely TN), you are entitled to a depaendant status, with the same validity and duration as hers. So, while you can enter on B2, its simpler to get a TD at the border, one time. Since
TN and TD allows living in US, no need to prove anything about Cdn ties. Forget B2 in your case, that is for tourists.
As to her situation, if she is going to live in US 9 months, she might as well commit and find full-time work there, as reba says, after 6 months, her Prov healthcare is at risk. You could both move and he would avoid Cdn tax altogether.