For the record, that's definitely not true, at least in the US (yes, I realize the original post involved Canada). While the X-rays used for passenger carry-on screening are low power and unlikely to fog film in a single or small number of exposures, those used for checked baggage (and Customs) screening are very high power and will readily fog even very slow film. Not all checked baggage is X-ray screened, but when it is, any film inside is virtually guaranteed to be ruined.
I tested this recently by putting a sheet of Polaroid (stored inside a Polaroid back to prevent the goop packet from being ruptured by the bag throwers) in my checked luggage before each flight I took. On about half of my flights (out of PHL, SFO, IAD and a couple of regional airports) the sheet was visibly fogged on arrival.
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