Many people are able to stamp H1 visa's once they become PR. Land in Canada, and get the H1 stamping same week or so. They are able to do this, because now that they have PR, Canada is their sort of 'home' country. I beleive this is the same case with F1.
Regarding ties to Canada, there is a requirement specified in the US Embassy as follows:
'Proof of ties/residence in country outside the U.S. which have no intentions of abandoning'
I remember doing this, when we were transfering H4 to F1. We attached a written document saying we have land, offshore company job for me (my wife has transfered to F1), she will do teaching in India, blah blah.....So I guess you have to prepare a good document saying ur intentions to stay in Canada once you finish ur studies....
I hope this helps. Appreciate if you could share your experience through out the process. All the best!!
Regards,
Thomas.