As an Australian, you do not need a visa for Canada, and you can stay for up to six months. This is regardless of whether you visited the US before and how long you stayed; they're separate countries, after all.
Your problem is going to be returning to the United States from Canada, because once you enter the US on a visa waiver, your "90 day" clock does not stop when you visit Canada or Mexico. You are thus quite likely to be denied entry to the United States, even if you have a connecting flight to catch.
Three possible ways around this:
- Fly to the US via Canada, so you don't need to return.
- Visit Canada before going to the US, since the VWP clock only starts ticking after you enter the US for the first time.
- Apply for a transit visa, so you can pass through the US without hitting the VWP limit. Rather painful (it's pretty much the same process as getting a "full" visa from a non-VWP country) and expensive too though.
And I hope you have a really good explanation for what you're going to be doing in Lake Tahoe for an entire ski season without working, because that plan is going to raise a few eyebrows at Immigration otherwise...