How to connect my Canon MP276 which connected with my Win7 to my SL?

Your biggest issue with the Windows 7 connection is having the correct driver on the Mac. The Canon supplied driver does not work when the printer is being shared by Windows. For this type of connection you need to look at an alternate driver, such as Gutenprint or PrintFab. Gutenprint is preferred because it is free and a version is included with Snow Leopard. But even the latest version of Gutenprint does not list your model as a supported printer. So you will have to test which of the other Canon drivers withing the Gutenprint suite will work with the MP276.

PrintFab http://www.printfab.net does list the MP270, which your MP276 is based on, so this would allow the Mac to print. The software costs €49 but there is a 30 day trial available so at least you can test it first.