Most canoe races these days require wearing of a PFD at all times during the race. Their insurance policy requires it. Many states, mine included, require everyone in small boats to wear one from 1 November to 1 May, and 100% of the year for youth under age 12.
During the Adirondack 90-mile canoe race, for the first 30+ years it was running (until NFCT took possession of the race), PFD wear was optional, unless weather conditions and the race director or DEC so mandated it. Theory was, with up to 250 boats in the race available to give aid, and with numerous safety and end sweep boats posted and observing each boat in multiple places throughout the course, the danger was minimal with a PFD in the boat but not actually being worn.
During the Yukon River races, 100% wear of a PFD is always mandatory while paddling in that 40F degree glacial melt water. in addition, once we enter the wide 35-mile-long Lake Laberge, we are required to remain within 200 meters of the lake's eastern shoreline. I remember one time when in a large voyageur canoe at (or even beyond) our 200-meter limit we were caught in a heavy following wind causing huge rolling white capped waves when I was in the bow taking splashing wash over the bow on to me, soaking me in that chilly spray. We kept on our straight course line downwind because any turn altering to the side could have been even more dangerous in that surf. The entire crew was concerned about our survival chances of swimming the distance to the shore if we needed to. We could see a number of other racers waiting it out on the distant shore. Eventually the shore came to us as we skirted in and out of relatively protected coves between jutting rocky outcroppings.
Much further downriver, at the Five Finger Rapids, a relateively short run often with 3+ foot high standing waves, it was common for a few boats to capsize and either self-rescue on an island just below the rapids runout area, or to be rescued by a safety boat stationed there. But that safety boat is only there for support during the relatively short (440 mile) Yukon River Quest. During the totally unsupported 1000-mile race, there are no safety boats posted anywhere on the river race course.