Recently got a canvas rucksack to use in the woods. It is untreated. Is there a way to treat it like the oil canvas filson uses or waxed canvas if it is already in pack form?

That sentence is confusing as shit but hopefully you all understood my question.

I've retreated my filson bag and it worked great, although I doubt it's ever going to be really waterproof.  

The key for me was to get A LOT of the oil/wax stuff.  Don't bother with Filson brand cuz it's too expensive and there's way too little in those little tins.  Bought a cheaper brand tat they had locally, that looked about the same as the Filson stuff...   a wax/oil blend is what it appears to be.  I did it on a hot day to help the melting and used a hair dryer and rubber gloves and some small scraps of cloth to saturate the canvas with the melted wax/oil.  Totally saturated.  Soaked in.  Then let soak in sun for days.  Wiped off and used.  Was a bit oily for awhile but it worked great.

I don't see the brand of wax/oil I used.  Even with that it was costly cuz it takes so much.  
Look at making your own:

http://www.chadsparks.net/2015/12/old-school-and-cheap-skate-oil-finish.html

I make my own using citronella candles and mink oil. Or soak it in scotchgaurd

Otter wax makes a good product I've used on a couple jackets and canvas shoes before.

I just rubbed some surf wax into some old boots and melted it in with a hairdryer.

works pretty well for stuff laying around the house.