George wrote

What didn't work was the time we were in Algonquin Park and we were
informed that our chosen route may not be passable due to low water
levels, on our permits they put down our chosen campsites and also
gave us some alternate campsites. We ended up going to the alternate
sites, but around 5 pm another party came around saying they were also
given the same campsite. It worked out in the end, as our site was
hugh and we were happy to share as was the other party.

After experiencing a number of alternatives I still prefer the
crapshoot of a first-come, first-serve paddle in and find a site
situation.

We're willing to schedule our trips to avoid putting in on Fridays or
Saturdays, so that we aren't in such heavy competition for sites, and
on long trips we'll often try to schedule our paddle out days for a
Friday or Saturday, in part so that a site opens up when it is most
needed, in part because such timing will put us back on the road,
re-supplying and en route to someplace else for a Sunday or Monday
launch.

One alternative I didn't care much for (although I recoginze the
management need for it in popular areas) is the oxymoronic
"backcountry reservations", especially when these reservations are
site-specific (ie, site #37 on Thursday night) as opposed to simply,
say, specific to a particular lake or area.

We had site-specific reservations in a couple of Ontario Provincial
parks a few years ago, and even though I had made the reservations a
few months before our trip I knew some of the sites were gonna be the
pits; when you call to make "backcountry reservations" months before a
trip and find that only one site remains in certain areas you can be
pretty certain there's a reason it's the only one left. Even more
maddening than reservations to camp at a damp, muddy, bug-ridden site
from hell is the realization that there are far better sites that
remain unoccupied because the folks who reserved them didn't show up
that day.