Looking for a bare bones guide to BTC

I've never dabbled in crypto up until now, but I'm currently a Canadian in the U.S. and I want BTC for the sole purpose of purchasing it with cash at a BTC atm, and then having the option to cash out to my canadian bank account at a later date, I understand I'm going to need a BTC wallet for this, and then a platform to sell my BTC at a later date, so 3 questions.

I want to prioritize ease of use, and safety over anything else, and don't mind paying moderate to high fees for this convenience.

1. What is the best wallet for this type of use, prefer something simple, a phone app, that can be used internationally, and is very safe/secure.

2. Which platform do I use to sell my BTC in Canada? I hear corn-base, or kraken are easy and near instant?

3. Any other things I'll need besides these 2 accounts, or any issues I could potentially run into eg. Do I need to declare this for tax purposes in case there is a lift when I withdraw my BTC etc? (All money has been legitimately won via poker, I just don't have a U.S. bank account, and don't like having tens of thousands in cash on me on the road.

Thank you very much fellas :)