Realistically, if you cannot afford to support yourself in Canada, how will you be able to in the U.S.? Do you realize that you won’t be eligible for disability here?
How will you pay for health care?
Will your fiance be able to add you to his employer-based health insurance?
And yes, it could impact your eligibility for an immigrant visa (public charge). It’s evaluated. Asked on the totality of circumstances, and your ability to earn and contribute is part of that.