"Around 1920" is important because prior to (I believe) 1920 Poland didn't exist, so if he had emigrated earlier he likely would not be a Polich citizen.

However, you're saying a manifest from 1946 shows his as having a Polish passport. This is very good because passports are issued for 10 years maximum (maybe a shorter time period back then) so apparently the passport he used in 1946 means he still was Polish at that time, and I would venture that the PP was issued by a Polish consulate in Canada.

Of course it's possible that he could have lost his Polish citizenship after 1946 (through becoming a naturalized Canadian for example) and in that case in would be important whether your mother was born before or after your grandfather lost citizenship. If she was born while he was still a citizen I don't believe she would lose it just because she lost it. And if she was born in Canada, the fact that she gained Canadian citizenship by being born on Canadian soil would have no bearing on her Polish citizenship.

As a first step I would contact the Polish consulate that has jurisdiction over the part of Canada he lived in at that time, and see if they have the passport application records.

Suggest yopu read all three Polish Citizenship Confirmation threads. They have loads of info by people who are more familiar with Polish Citizenship than I am.

 

I am in a similar situation. The Polish government wants lots of information however finding a Polish passport record is golden. I asked the Polish Consulate in Vancouver about doing a Polish passport search and here is the reply.

"I regret to inform you that search for the requested records it’s not possible. Most of the records were destroyed during the World War II."

I recommend writing your consulate. If you get a different response let me know because I want do a Polish passport search.