They can. Two entities owned and controlled by the same group of individuals, each owning approximately the same proportion of each, are affiliates for L-1 purposes. No parent company or cross-shareholding is required, but the proportions must genuinely align.
Common owners can be enough
Hypothetical example: two Hampton siblings each hold fifty per cent of a Canadian machining company and fifty per cent of a U.S. company, with no shareholding between the two businesses. Read against the parent and subsidiary language, that looks like a dead end, and some owners abandon the idea there.
The affiliate limb of the definition is designed for exactly this structure: the same group of individuals owns and controls both, and each of them holds approximately the same proportion of each entity. What the petition then has to do is prove it rather than assert it, with share registers, a percentage table for both companies and, where there is more than one class of shares, an explanation of who controls the votes. The claim is simple; the evidence has to be exact.