Remember that McDonnell-Douglas CF-101s were not the RCAF's first choice for interceptors, rather CF-101 Voodoos were purchased after a long series of mistakes.
Mistakes started with RCAF greed demanding a "made in Canada" fighter: the CF-100. CF-100 Canucks proved capable long-range, all-weather, subsonic, interceptors, on a par with Sea Vixens.
Then the RCAF got really greedy and ordered the supersonic Avro CF-105 Arrow for a similar interceptor role. Problem was, Avro of Canada needed to develop a new airframe, 4,000 psi hydraulic system, new engines, new missiles, new fire-control systems, etc. ..... far more than Canadian tax-payers were willing to pay for during the 1960s!
After the Arrow program collapsed, the RCAF bought Bomarc missiles to plug the gap in North American defenses. No one seriously believed that Bomarcs were an adequate defense, so Ottawa and Washington began negotiations about Canada taking over the Pine Tree Line, buying second-hand USAF interceptors, loaning instructor pilots, etc.
The USAF was phasing out (single-mission interceptors) F-101 and replacing them with (dual role, fighter-bombers) F-4 Phantoms, so it was an easy exchange for the USAF.
The USAF also enjoyed dozens of exchange officers teaching young American limits to fly during the Vietnam War, when the USAF could barely spare experienced pilots from SE Asia.