Can anyone speak to the churnability of the BMO Air Miles World MasterCard?

My wife signed up for it mainly for the bonus miles + 25% discount on booking rewards, which on a family booking adds up to a substantial number of points.

Now our winter holiday is out as my wife is due to give birth around New Year's. If she cancels the card this fall, what are the odds that she can cancel, sign up again and get the bonus? Or could I sign up and just use her AM number? (I currently have the BMO World Elite MC, but have never had the BMO AM card... other than this one card, I am not that familiar with BMO and its CC practices.)

I'd be grateful to hear anyone's experiences with this... what I read could affect my strategy for accumulating Air Miles