I am going skiing shortly after Christmas and I have a thick canvas (65% polyester, 35% cotton, brushed) coat that I need to waterproof. Is a wax more efficient for waterproofing than a spray for this situation? I'd like to avoid wash-in waterproofing as well.
It's hard to tell without all the details. As a rule of thumb I'd apply whatever was applied to the coat originally.
If it didn't have a coating at all then the waterproof spray is likely the best option. The spray is likely going to produce the best result. Wax can discolour and make a jacket stiff. These day's wax is only used on "wax jacket" type coats. Whatever you do don't apply wax to any breathable jackets, it will likely ruin them.
As a side note you said the spray was a "fluropolymer compound". Just as an FYI these compounds are frowned upon these days, PFOA type compounds (which this almost definitely is) produce significant environmental and health concerns. Most manufacturers have moved to biodegrable, more environmentally friendly compounds these days.
e.g. see this Goretex statement
If you can, buy a block of candle wax at a hobby store candle shop. Then buy dry cleaning fluid. Carbon tetra cloride is best, although you may not be allowed to buy that in the U.S. Put your wax in that to dissolve, as much as it will in 24 hours. Paint it on with a brush or spray bottle. This is the best I have found to use.
For a light wax, Pledge furniture polish works well but it doesn't last as long. In 3 days the scent will leave. This is a 3rd world tropics solution. Here we can not buy camp dry & such as you can.
On my duster long coat which is 65% cotton I find this works well. It's also good for water proofing a nylon tent.
If you just need a few days of water proofing, try the Pledge. Reapply in a few days.
Yes for cotton or poly cotton jackets wax is far more effective at waterproofing a coat. An easy way to reproof such a coat is to rub a candle on it until it is covered in white wax. Then take a hair dryer and melt the wax in. You might need to repeat the process to make it really water proof. The sprays like Nikwax and Fabsil tend to wear off after a few weeks. But with melted in solid wax the waterproofness should last for at least several months.