concur -not sure how it's listed in Canada either, but Custom Trim in US is not the same as Highlander. "Special Promo Package" or something like that, as Special K highlighted, indicated a Highlander truck - and that included the plaid seat. But the seat trim also normally appears on the SPID of a Highlander (or could be ordered separately as mentioned) - but either it would show up on the SPID as "Orange (or Green, or Blue or Gray) Plaid seat trim... etc.
But yes - that IS a plaid seat and it is the type associated with a highlander.
Why buy a whole truck for the seat? Why not just buy a new highlander seat cover from one of the vendors - Truckseats, perhaps? it's a nice truck, I'd keep er all together, and then STILL buy a separate seat cover for whatever truck you currently need it for