VWP or B2 for short stay in US on way to Canada?

My family and I (Australian citizens) are travelling to Canada for 4 months, with a stop-over in the US for 3 days. Our return flight leaves direct from Canada, we will not be transiting through the US on our way back to Australia. As Australian citizens, can we just enter the US on the Visa Waiver Programme or will we need to get a B2 visa? It sounds like legally we need a B2, but anecdotally a VWP may be fine..? It is quite costly and inconvenient to get a B2 visa for just 3 days, but my partner is quite risk-averse especially given the tightened Immigration into the US..! Any recent experiences would be helpful. Thanks
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Can I travel to Canada with US B2 visa?
In case you plan to visit the United States, then you most certainly need to apply for a visa. That is, of course, if you are not visa-exempt or your country of origin is in the US Visa Waiver Program.Do you need a ESTA to transit from USA to Canada?
ESTA required for transfer to Canada If you are flying through the United States to Canada, you need to apply for both an ESTA as well as an eTA. Both travel authorisations can be applied for through this website: ESTA application and eTA application.Is Canada under VWP?
Permanent residents (landed immigrants) of Canada must have a nonimmigrant visa unless the permanent resident is a national of a country that participates in the Visa Waiver Program (VWP), meets the VWP requirements, and is seeking to enter the United States for 90 days or less under that program.How long can you stay in the US with a B2?
B1 and B2 visa holders are allowed to stay in the US for up to 6 months at a time. Each visa application will be assessed on its own merit, and the adjudicating officer may grant a stay of less than 6 months \u2013 this is the maximum period for an initial stay under the B classification.About Visa Waiver Program | How to travel in US without a visa | Visa Waiver Program USA 2021 | DHS
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