Double check whether your airlines allow you to travel alone, including international and connections, at age 12. You miight need to be officially registered as a UM (unaccompanied minor, with paperwork and fee paid by your parents--get to the airport early--and papers filled by your grandparents for the return). You might need notarized permission letters signed by both parents. You should also have a document authorizing medical treatment in case something happens, sometimes called a medical power of attorney document. These might need to be officially translated by a translator certified by the Chinese embassy in Canada.

If you have dual nationality, be sure that your parents fully understand its implications. You need to know which passport to use when, probably China to enter and exit China and a Canadian passport to enter and exit Canada. Otherwise, make sure that you have the right visa, either for a family visit to China or to re-enter Canada.