Take some time to read through the guide provided by CIC. It will explain the process. To summarize though, you will send your sponsorship application and your wife's permanent residency application in together to the federal government. Once your sponsorship is approved you will get notice from the federal government. At that point in time you and your wife will fill out the required sponsorship application and Certificat du selection du Quebec application that must be submitted to MICC (there is more info about this portion of the process on the Immigration Quebec website).
Two points I want to make:
1) Seriously consider doing an out land application for your wife, even if she is already in Montreal with you. I was in Quebec throughout my entire application period with my husband, but I still did out land. Check application processing times. Unless your wife is from a country with a wait time of over 1 yr, she should probably do the out land application. The only benefit of the inland application would be her receiving a work permit after your sponsorship is approved (which takes about 1 yr at this point). Also under an out land application she is free to leave the country during the process, whereas an inland application shouldn't leave during the process, because denial of reentry results in the cancelation of the application. Finally, whether she does inland or out land she must maintain proper legal status the entire time she is with you in Canada.
2) Really take time to read the guide from the federal government and accompanying checklists, because there are a few documents you do not need to fill out as the sponsor since you will be doing your undertaking with the Quebec government.
