You still would have time to make it to Canada from Walker Pass if you’re able to average slightly more than 20mpd (including zeros). Walker Pass is almost exactly 2000 miles from the Canadian Border.
It would be hard to start out averaging high mileage through the Sierra without being in top shape, but you can make up a lot of ground in NoCal, Oregon and southern WA. One option is to just head north from Walker and then flip if you have to later on. The decision to flip is really difficult to make though…
Last year some NOBO’s flipped on the advice of some very PCT savvy hikers (Billy Goat & a few others), but ended up getting hammered with cold wet weather coming SOBO from Canada in early September & then we ended up having an incredible Indian Summer in the North Cascades in October. So… the advice was probably good (statistically speaking) but it ended up backfiring on the hikers.
So, my advice
is to pick out an option that you are comfortable with & is convenient logistically speaking & then just go for it! There are so many variables on a thru-hike so you can never account for everything & you sometimes have to take risks.
On my PCT hikes, my primary goal or top priority wasn’t to complete the thru-hike. In fact, I’ve always felt that if the destination is the primary goal, then some of the journey or experience is sacrificed. So I always try to hike every day like it’s my last day hiking - enjoy it to the fullest. I don’t want to compromise even a single day of the journey (ie. ‘I’ve got to make so many miles today…’). I have been fortunate to finish the PCT 3 times, but the completion was really just the icing on the cake (& the icing itself is bitter sweet).
Have a great journey & enjoy every day on the Crest. Ideally, thru-hiking should be more about smiles than miles.
Happy Trails!
freebird