You can vote most days at most Elections Canada Offices across Canada before April 22nd. There's also the advanced polling days as well and other ways to vote.
The NDP vs Liberal debate is often a really easy one to solve if people are torn- check 338 Canada to see if the NDP have a roughly equal or greater than 1% chance of winning that riding. If they do, vote NDP.
That might sound like a very generous rule for the NDP but it actually amounts to about 17 of 343 ridings.
Just remember you're not voting for Carney, you're voting for a local MP, if the liberals aren't viable in your riding you're essentially throwing the vote away.
If Doug Ford somehow didn't win the recent election, Poilievre would have a lot better chances in Ontario. It tends to be a thing in Ontario where people don't want the provincial and federal to be the same party.