Quote Originally Posted by Miss Z
I can't really answer the first and last question as I'm not a western rider, but I'll have a bash at the other two.

Does lifting your hands make you sit straighter when cantering?

Yes, that is correct. A lot of riders, myself sometimes included, allow their weight to fall onto their hands in canter. This subsequently leads to the rider leaning forward and their weight out of the saddle as the hands rest on the horse's withers. This isn't comfortable for horse or rider and often leads to loss of stirrups, sore knees, and falling off! By lifting your hands, you stretch down into the stirrup more and push your weight into your heels, thus causing your body to sit up straighter. It can be challenging to keep a constant hand position throughout all paces but it is very useful to be able to do.

Also...does jumping jumps with one stride in between them help slow your horse?

I'm not sure 'slow' is the right word. It makes your horse more attentive and obedient to the aids for sure, but gridwork is not intended to slow your horse down. The secret to jumping well is a confident and well-maintained rhythm on the approach, playing about with the speed and length of stride usually results in a refusal. The jumps should always be placed the distance apart of the horse's natural canter stride, so as a rider it is your job to not interfere with his rhythm but instead to be there to guide him over. I find gridwork useful, but bounce fences (jumps with no strides in between, just taking off straight after landing) is even better.

Hope that helps.
Your english riding is so different from here Maybe we need to just make up Canadian riding.