In 69-70 the Canadian cars have their own fender with the wheel opening moved one inch closer to the cowl to correct for the chevy frame having one inch less distance from the frontwheel center line to the O line (cowl). I suspect they didn't do that in 65-66 because the wrap around bumpers would have needed changing too, they just let the wheel be an inch back in the wheelhouse. The added problem for some years was when the wheelbase difference between Pontiac and Chevy B bodies was more than 2 inches.

For example in 69-70 Pontiac's were 122" versus the chevy at 119", this forced them to put the rear axle 2" forward in the rear tub (quarter panels were shared between Catalina and canadian cars) instead of one. Similar situation in 59-60. 61 was the only year where American and Canadian Pontiac's had the same wheelbase (except bonneville-starchief). Having the same wheelbase as chevy that year really hurt Pontiac sales in the US so in 62 they added an inch to 120. In 65 they added another inch to 121 and 122 in 69.

One improvement along the way in Canadian cars (not sure which year) was when chevy started changing the offset of the wheels to get rid of that look Bunkie called "gorilla on roller skates" that is very noticeable in the 59-60. The difference between chevy Impala and Pontiac track went from 3.5 front and 5" rear in 1959 to only 1" front and rear 10 years later.

Canadian Pontiac and chevies always had the same track but they cheated in the brochures because chevy listed the track with the base 6 cylinder which had narrower wheels while the Canadian Poncho brochures listed the track that an 8 cylinder car would have (which was wider thanks to the wider wheels used with a V8. American Pontiacs had wider track due to the wider Pontiac chassis (including longer rear axles).

GM often was loose with facts on these specs, perfect example is the rear track on 68-72 cars with the BOP 10 bolt, they listed Pontiac A body cars (GTO etc) as having 60" rear track but the identical diff and wheels on a buick skylark were listed as 59" The actual track was 59.5" with 4 wheel drum cars and 59" on cars equipped with discs up front (disc cars used a wheel with 1/2" more positive offset for caliper clearance).

By the late 60's the actual 4-5" extra of Pontiac (American) "Wide Track" was just a marketing myth of anywhere from zero to once inch of extra track.