Staying in US on ESTA/VWP, then entry into Canada and return to US, then returni...

Me as a Hungarian citizen planning to stay in the Usa with the Esta/vwp for about 85 days than drive to Canada stay for about 3-4 weeks and drove back to the Usa and stay another month for participate on an event and sell the vehicle. After reading that a Canadian or Mexican trip does not reset the 90 day clock i am questioning that my plan would work out. In 2018 i did a roadtrip in the Usa on esta. Staying in the country for exactly 90 days, driving to Mexico for the winter staying there about 4 months and drove back to the usa and they stamped 90 days in my passport. So i am not sure if they would give me hard time re-entering after a Canadian trip.

After reading that a Canadian or Mexican trip does not reset the 90 day clock i am questioning that my plan would work out.

"Not resetting the clock" is an oversimplified shorthand for what actually happens. In fact, the regulations say that an officer may readmit someone for the balance of their initial 90-day period under certain circumstances, including the condition of having traveled no farther than contiguous territory or adjacent islands. But this isn't required; an officer can also give a new 90-day period of admission if that is appropriate, and the provision does not apply at all if the second application for admission occurs after the end of the 90-day period.

The itinerary you propose is therefore compliant with the terms of the visa waiver program, provided that the officer admits you the second time. Your plan to spend nearly four months in the US over the course of five months or so could prompt the officer to look at your circumstances more closely. If you can convince the officer that you're really planning to stay only for one more month, you should be fine; your earlier similar trip should help with this, since it was a few years ago. You're probably also more likely to be admitted since, as it seems, one reason for going back to the US will be to catch your flight home to Hungary or wherever.

Your alternative is to get a B-2 (or B-1/B-2) visa, for which the initial period of admission is typically six months; in that case, your plans could not be seen as trying to game the system because the visa would cover the trip even without the visit to Canada. If you have time to make the application (and can get an appointment), this should give you slightly more peace of mind, but if you can't, you should probably just stick with your initial plan to use the VWP, perhaps making a contingency plan in case you have trouble getting back into the US.

The relevant regulation is 8 CRF 217.3(b):

Readmission after departure to contiguous territory or adjacent island. An alien admitted to the United States under this part may be readmitted to the United States after a departure to foreign contiguous territory or adjacent island for the balance of his or her original Visa Waiver Program admission period if he or she is otherwise admissible and meets all the conditions of this part with the exception of arrival on a signatory carrier.

Note the use of "may," which confers discretion. The signatory carrier exception means that a traveler can still qualify for this provision even if flying into the US or arrive by sea on a carrier that does not participate in the VWP.