How does the TREK 700 Ti compare to the 600mL Ti mug?
600 - 3.75(d) x 4(h), 20 oz capacity, 2.9 oz wt.
700 - 4.125d x 4.37h, 24 oz capacity, 4.5 oz wt.
Also, will the small fuel canister(SnowPeak) fit inside the 600mL mug?
Yes. In fact, the 600 will house a Gigapower stove and a small Snowpeak canister (stove goes in first, then the canister slides in upside down -- perfect fit with nothing protruding out.
Take a look at AntiGravityGear's 3-cup aluminum pot. Light weight and cheap ($8). I just ordered one, so no direct experience, but have read lots of good reviews.