We had the same issue earlier this year. We were away for a month but it spanned a billing period cutoff so there was effectively no cap.
We are with Rogers and the 'solution' was the Infinite Plan with Unlimited calling, texting & data in Canada & the US. It is not an inexpensive plan but makes sense for our needs. It does not come up as a Travel plan when you search. The agent mentioned it when we called.
I find the plans unnecessarily confusing, I suspect intentionally. They always seem to be changing, so what makes sense at one point does not later. They did have a promotion for this plan when we signed up and we also got a discount for a professional membership.
It would be worth phoning, maybe more than once depending on the agent you get, to see what plans FIDO has that include calling, texting & data in the US and what discounts are available.