Exploring Citizenship in Multiple Countries

Hi everyone, first time poster!

I'm exploring dual citizenship by double descent in the following countries:

-UK -Greece -Canada

I'm a US citizen born in the states in the 90s. My grandfather was born in England in the 1930s, and my grandmother was born in Greece in the same period. They eventually married in Greece before moving to the US and getting dual US citizenship.

My father was born in the US, and in 70s his parents separated and my grandfather moved to Alberta, CAN and held citizenship between the 3 countries. (At the time of my father's birth, his dad was British/US dual citizenship but did not hold CAN citizenship yet). When I was born, my grandfather was living in Canada.

My father at one point tried to get British citizenship, but got held up because he needed his parents original marriage certificate in Greece. It might be possible to track down, but it would either require going to Greece or hiring someone there to find it.

My grandfather died a few years ago, so I no longer have a living relative in Canada. But I'm very interested in exploring citizenship options.

So, questions: Do you think any of these pathways seem easier/harder? Do you think it'd be easier to first get my father's citizenship before pursuing citizenship as a grandchild?

Any input/advice is appreciated, thank you!!