I have both. To Slavex's comment my experience is not quite the same. I had an issue with my M2 5" PPQ and I sent it to North Silva. They replaced the sear box and had the gun back to me within 14 days which is pretty good given the Post Office consume 10 of those days.
To the OP for mounting an Optic I can tell you my Optic is now on my SIG X Five. The gun has a bull barrel and a tungsten weight in the grip. The additional weight soaks up recoil resulting for me, less muzzle flip which leads to faster re-acquisition of the red dot. The gun is a tinker toy gun and you can turn it into a any size of gun your heart and your wallet desires. I think it will dominate the Optic IDPA Division if that Division takes off. There is lots to like and not much to dislike.
Having said that there is the PPQ Match. It has the best trigger of any striker fired pistol out of the box.....PERIOD! Walther advertises a 5.6lb trigger pull. My two PPQ's each came with 5.6lb trigger pulls as tested on a Lyman trigger gauge. Folks in the US report the pull after a thousand rounds or so will fall to around 4.6lbs. The gun also has developed a well earned reputation for accuracy. Off a rest it shoots inside an inch using my cast bullet reloads as does my CZ 75 Shadowline. There is a member here who uses his Match for PPC shooting out to 50 yards. That in itself is high praise. If you handle recoil better than a 74 year old slow moving shooter and lots do, I would not hesitate buying the Match and installing an Optic on it. I believe based upon my experience the Match has the edge on accuracy over the X Five. Understand that is a VERY subjective statement. Both pistols exceed the mechanical accuracy requirements of IPSC or IDPA. One real advantage the Walther has over every other pistol I know of involves the changing of the sights, both front and rear. Both sights can be removed and replaced in 10 minutes or less with the use of a screwdriver. That may or may not intrigue you.
Take a deep breath. Walther is coming out with an all steel version of the PPQ Match. I predict the gun will be a player ,if not the player, in the striker fired side of IPSC Production Division. Early reports are that the gun enjoys the same trigger/striker group the polymer PPQ has and enjoys the same mechanical accuracy. It may well end up taking on the Glock/M&P hold on IDPA SSP Division although the lunch bucket crowd in IDPA tend to hang closer to what they carry or what they have from my experience. The gun is just now being let out in the US. I suspect the gun will sell for around $1,500Cdn or more up here. Striker fired, all steel, outstanding trigger, top tier accuracy and Optic ready.....not much to complain about.
My verdict. It's a tie. Either will serve you well. There is no need to change anything on either pistol,unlike some who rely on the after market boys to finish their guns. Support and warranty is weak with the Walther in Canada. That may be an issue...it was not for me. The SIG defines the modular concept. You could spend your kids University money on combinations available to you. Well living in Canada half are deemed to be death guns and are prohibited due to barrel length.
If you can contact an IPSC or IDPA club in your area and see if any of their members own and shoot either pistol. Folks in both sports are always willing to allow folks like yourself to try their guns. If neither is close at hand perhaps a commercial rental range may offer an example to use. Both pistols are presently at the top of the striker fired food chain along with the CZ P10 and S&W Gen2 M&P. I am not certain the CZ is out yet in a FS version but will be along soon.
Take Care
Bob
PS Soley Canadian makes a great holster for either gun along with mag holders.