Your grandfather was Polish, which means that one of your parents were Polish, which means that you are Polish, by birth...As long as no one formally renounced their Polish citizenship.
You're not seeking out a new citizenship, you were Polish when you were born. Go get your passport. Canada recognizes dual citizenship.
cic.gc.ca/english/resources/publications/dual-citizenship.asp
If you, your parents, your grandparents and your spouse, if you are married, were all born in Canada, and you have not become the citizen of any other country, then you most likely possess only one citizenship: Canadian.
However, if one or more of these people were born outside Canada or acquired another citizenship, this might result in your having dual citizenship, depending on the laws of the countries concerned.