Genealogy /
Grand mother's maiden name? She was born in Poland. [3]
You have a start to what you are trying to find. Yes, it will be difficult. Where did her 1st husband die? If you can obtain his death certificate, while this may not provide an immediate answer to your question but may lead to a general area where they may have gotten married. Also, another thing to consider is her religious beliefs. That would also help to narrow down the search.
Was she married before or after she immigrated? When did she obtain Canadian citizenship? Did she get this before or after she married the 1st or 2nd time. Another source of information to follow up is the census records. Also ask yourself did she have children by the 1st marriage and which are from the 2nd or all the children from which marriage. By trying to put this information into perspective it may help to find her maiden name. Good luck. Did she ever keep up with her literacy in Polish by writing to someone back in Poland. If so, do the letters survive? While the person that wrote to her may be dead as well by now, but those letters may give clues as well by backwards engineering that persons answers to what she may have written.