Okay....canvas is usually cotton. Cotton, unless you're using a substantive (no need for a mordant, such as madder roots or indigo) dyestuff need something to make the fibres receptive to the dye. Usually, if you want a good colour and not a kind of wishy-washy *stain*, cotton is alumed to grab hold of some of the tannin from the next part of the process, tannined and then re-alumed; and all of this is before it ever sees a dyebath
Walnut hulls are a substantive dye, but they can be expensive. So, if you want to guarantee a good colour from a lesser quantity of dyestuff, make the cotton able to grab hold of as much of the colour as possible.
Alum the material before it's dyed and if you're really up for the whole tannin then re-aluming, great. If not, boil up the oak galls or bark to make a tannin liquor, steep the fabric in that, then boil it up in the dye liquor, or at least bring it up to heat and happ it up to keep it warm as long as possible.
Ink; Oh this'll be pretty permanent

but if you add a little iron water to it, it won't budge

To make the iron water add some vinegar to steel wool and watch it rust

just add the strained liquor to the ink mix. The old ink recipes use gum arabic as a slight thickener and it helps the drying a bit too.
I find walnuts, if really finely powdered, kind of dissolve in the dyebath, but they can be a pain to strain out. Paper kitchen towels in a sieve work, if a bit slowly. Let the bath settle first and then strain carefully to avoid the worst of the gunk.
I'm curious now, what are you up to? Duluth packs?
atb,
mary