I don't know who if anyone your wife used for an attorney, but he/she should have advised her that an "adjudication withheld" entry in Florida is pretty much the same as a conviction. All it really means that the person is guilty of the offense charged, but will be allowed the right to have the record/"conviction' expunged after a certain time.
It's unlikely that Canadian Authorities will see the finer points in this situation...your "plan B" to take the Alaska Ferry out of the U.S. without setting foot in Canada is probably the best one.
