Again, I could be wrong, but, I believe the 200' x 85' rink was originally regulated by either the NHA, the PCHL, or the NHL (or perhaps an earlier predecessor of those pro leagues). And then other North American leagues conformed to that rink size. Meanwhile, across the pond the IIHF independently regulated the 200' x 98' rink, and in Europe it became the standard.
The 200'x85' rink was standardized by the NHL in 1929. The older rinks before then were all about the same size—Ottawa Auditorium was 200x80 as was Dey's Arena before it, Mutual Street Arena in Toronto was 200x80 and so too was Hamilton's Barton Street Arena. Westmount Arena in Montreal was 200x85 and the Forum was too. When the Bruins joined the NHL in 1924 they played at Boston Arena (still standing and known today as Matthews Arena), which was 200x80 as well. Pittsburgh's Duquesne Gardens was capable of hosting an enormous sheet well over 200' long but it was reduced to 200' when the Pirates began playing there.
The first building that was smaller was Madison Square Garden. The third building to bear the name, opened in 1925 to host the Americans, had a surface only 186' long (by 86' wide). It was designed primarily as a boxing venue. Teams were added in Chicago and Detroit and they would build new arenas too. Detroit's Olympia was 200'x83' but Chicago Stadium was only 188' long, and Boston's new Garden was 191'x83'. Rather than allow arena-builders to come up with their own (smaller) sizes the NHL codified the 200'x85' size in 1929, following the example set by the Westmount Arena and Montreal Forum. Maple Leaf Gardens and every arena built for an NHL team since has been 200'x85'.
I believe the Boston Garden was the last of the old, smaller rinks.
The Aud in Buffalo was 196'x85' (and not built for NHL hockey), and was used by the Sabres until 1996. It just barely beat out Boston Garden and Chicago Stadium for the title of "last of the old, smaller rinks".
(FYI Pittsburgh Civic Arena (which was also not built for NHL hockey) was 205x85 when it opened; it wasn't reduced to 200x85 until 1974. The only other arena I know of off the top of my head that was used for NHL hockey and didn't meet the 200'x85' standard was the Cow Palace in Daly City, California; the Sharks' first home was only 185'x85'.)
As far as I know Hockey Canada has nothing to say about ice sizes in the rules but have notations in the rules about zone, goal line sizes/depths to accomadate different sizes.
On the contrary, one of the very first rules in the book is rink size. You're right that the rules about where to mark the zone lines and such are written to accommodate different rink sizes but the rules (for new arena construction) are that the maximum is 200x100 and minimum is 200x85. The CAHA, forerunner of Hockey Canada, adopted 200x85 as its recommended size in 1938.
For the record the IIHF rule book doesn't have a hard, set size. It calls for a maximum of 61 m by 30 m (a little over 200'-1" by 98'-5") and minimum of 56 m by 26 m (~183'-9" x 85'-3"). Anything in between is acceptable, but IIHF-sanctioned competitions are supposed to be held on surfaces 60-61 m long by 29-30 m wide.
Not every country outside of North America follows the IIHF 60x30 rules. In Finland for example most arenas are 58 m x 28 m (about 190'x91'-10").