Diemaco, I find your choice for a moniker interesting. You do realise that this is the name of the company that manufactures firearms for the CF? I‘m confused about the message you‘re attempting to make as you seem to know very little about firearms.
I‘d suggest you go to your local library and read "Jane‘s Infantry Small Arms." It‘s a good place to begin. You‘ll have more information than you‘ll ever know what to do with and then you‘ll be in a better position to decide the questions you‘re apt to ask in the future.
There have been a few opinions written in this post that are just that, opinions.
For the record, Para Ordinance (a Canadian company) markets a nice series of .45ACP pistols that have larger magazines.
http://www.paraord.com/pages/index.html
The Glock is a pistol with a strong reputation and is hardly cheap - approx C$1000+.
As for the 9mm v. .40 S&W v. .45ACP. There is much written about this. Law Enforcement Publications and Sporting magazines (Guns & Ammo, etc...) have been debating the pros and cons of each for years. Bottom line. The NATO standard is currently the 9mm Parabellum (Luger). It is a proven round with a long history. (i.e. lots of guns and ammuntion types, 9mm bullets can be in many weights, everything from 95gr to 185gr; and types, Full Metal Jacket to Hollow Points to Semi-Wadcutters. The velocities vary with the weights and the power loading, eg. 155gr FMJ+P+ translates into a powerful load propelling a heavier 9mm at a fair velocity, this round would penetrate)
Something you need to understand is that there is no such thing as a magic bullet. As the person who is firing, you need to be confident in your firearm (train, care for, become proficient and confident, etc...). Accuracy matters so much more than the bullet most often. You want the bullet to penetrate into the body, preferably causing as much trauma as possible to the vital organs. Whichever calibre you use, this is the goal. You want to drop the guy before he has a chance to drop you.
The thing is though, are you wanting to defend yourself? (Get a shotgun) Are you in law enforcement? (The sidearm is your primary "defensive" weapon) Or are you in the military? Take care of "your primary" weapon, your rifle. The sidearm to a soldier is a backup.
Beyond that, it‘s all personal preference. I personally favour a Colt 1911 SA .45ACP w/ a few after market modifications. There are many companies who specialize in such things. Kimber makes a nice .45 for the LAPD SWAT for example. That‘s my pref. In the field, if passed a 9mm BHP or a Sig P225, then I hope I have enough time on the range to become proficient with that. (and my C7)
Hypothetically speaking of course as I have to remind myself that I am a civilian again. (for the time being
)