Would this work?

I currently do not have a sump on my 29 G fish only tank. I am going to eventually make it a reef tank but due to circumstances not under my control I can't. I just came up with an idea for a sump for my tank and an algea scrubber which will help me get rid of my UGF. Basically redirect a powerhead out of the tank and into a 10 gallon (doing the algea scrubber at the end of that plumbing. Then using a canister filter to push the water back into my tank. I was curious to what I could add or remove from this idea to make it more efficient. The below picture is a sketch of the idea.

the canister may suck the water out too fast unless you can regulate the return flow, but looks good on paper

In my experience, canister filters don't have enough power to push water up from a sump back into a display tank. You will need to get an actual return pump.

Also, you need to get an overflow box. You will never get two pumps, even identical pumps from the same manufacturer, to pump at the same rate.

+1. With 2 pumps you will either flood the sump or the tank.

Is there any way to add a sump to an non-drilled 29 G with tempered glass?

Yep. A hang on the back overflow.