Hi syed,
it is not written there, yes, but you can do it! At least extend the permit, and if you have a new one, you can even get one at the border, doing the flagpoling. You can send it via Paper Mail,(slow), or Online (possibly 2-3weeks) , or at the POE (border) about 30min. I did extend my WP end of july. I took all the necessary docs with me, 150$ in cash....a friend drove me to Bernard Lacolle Crossing (30min from Montreal) and that was it. A WP extension done at the border at jaw-dropping speeds compared to paper application. If you want, have a look for another forum member here called "Beakster", he was actually helping me out a lot with this!
I'm not sure about one more option (gossip!) that you could take an appointment in Montreal at Rue St. Antoine Immigration to get it done, but the appointments can take a while, 4-6 weeks later. But this is NOT confirmed! BUT it is confirmed to get your Permanent Residency (Landing) done there !! Again, Appointment 4-6 weeks, depending on workload over there.
does it help?