Canadian no-coiner looking to get started

Just starting my research to get started. Yes, I'm late to the game, but better late than never, imo.

I have a few questions, and hoping some other Canadians can enlighten me. I was thinking of just arranging to purchase $x cdn per month to buy bitcoin. Probably use coinbase as the exchange and will get a hard wallet (ledger). So say if I wanted to turn some of my bitcoin back to cash, what needs to happen in terms of doing your taxes if:

a) Your investment of $1000 cdn is now worth $2000 and you withdraw half?

b) Your investment of $1000 cdn is now worth $500 and you withdraw $250 ? Nothing? Not a practical situation as I wouldnt do this, but just trying to understand what is considered profit.