Should our business register a .com or a .ca domain name?
If available, you should register both.
If your business is intended to have a global reach, then your main website should be the .com, and your .ca domain name should point, or be redirected to, your .com website.
If your business is intended to have a Canadian market, then your main website should be the .ca, and your .com domain name should point, or be redirected to, your .ca website.
(google.com and google.ca will usually provide different results for the same search term. Browsers with a Canadian IP address are automatically shunted to google.ca)

Is not "myreallylongbusinessname.ca" domain name the best to use for my business website?
There is no question that a business should register their business name's domain name.
However, a long business domain name should be 'pointed' (forwarded or redirected - at no cost) to a business site with a domain name that is SEO-friendly (see below).
Many Canadian companies have also begun to catch on to website marketing using a strategic domain name.
Some examples are:
allyouneedischeese.ca ( Dairy Farmers of Canada )
backactive.ca ( WCB )
bringitoncanada.ca ( Playtex )
bugsmart.ca ( SC Johnson )
freshenergy.ca ( Subway )
fruitsandveggies.ca ( Canadian Produce Marketing Association )
getyourbuttseen.ca ( Colorectal Cancer Association )
getmycard.ca ( Capital One Mastercard )
freepillow.ca ( Sleep Country )
justdontfall.ca ( Acorn Stair Lifts )
livewellsavewell.ca ( Johnson & Johnson )
loveyourheart.ca ( Becel )
not4me.ca ( Health Canada )
pumptalk.ca ( Petro-Canada )
realfoodmovement.ca ( Hellman's )
thinkbread.ca ( Dempster's Bread )
worksforme.ca ( McDonald's )

Who can register a .ca domain name?
The .ca ccTLD (country-code Top Level Domain) is intended for Canadians to market to Canadians using their Canada domain. Foreign entities with a legitimate interest can register a .ca to market to Canadians. (See CIRA's website for details)
The regulations of the .ca Canada domain were markedly changed in the year 2000. At that time, there were 60,000 .ca domain names registered. There are now over 2,000,000 registered .ca domain names.

Why are resale domains so expensive?
( View this year's top reported domain sales at dnjournal.com )

The short answer is: "supply and demand."
The long answer is: "They're not." Businesses of size usually have a techie on staff that, hopefully, appreciates the domain name field. Smaller businesses should absolutely invest in a consultation that involves (in order):
1. Domain name strategy
2. SEO (Search engine optimization, including keyword analysis)
3. Website design

Shouldn't website design be #1 on the list?

Absolutely not. While a business should avoid a horrible website design, what is the point of spending $10,000 on a website design that is seen by few people (which happens much too often).
(This would be comparable to having created a magnificent brochure or catalogue, and never having it distributed.)
Contrast that with the design of the most popular site on the internet - google.com - which is simplicity itself.

What is an example of good SEO?
A search in Google for "dentist Toronto" produces www.5000yongedental.com as the # 1 result. Google Adwords indicates that there are 27,100 searches per month for the term "dentist Toronto." Alexa indicates that www.5000yongedental.com receives 18.35 % of the search traffic for this term - therefore, 4972 searches PER MONTH for this term alone. Kudos to the SEO work.

What is the better investment?
What is better - paying what is essentially a ONE-TIME cost for good SEO work generating the above results?
(If that site and SEO cost $20,000, and the cost was amortized over 10 years, then the cost would be $2,000 per year.)
Does being buried among the dozens of full-page Yellow Page dentist ads costing $20,000+ PER YEAR ( which is 10x the annualized cost of the website ) generate 10x the results, or 50,000+ visitors per month?
At the end of the year, the Yellow Pages directory is replaced and the previous year's advertising is gone.
The website remains year after year.

What suggestion would be made regarding www.5000yongedental.com's domain name?
A good domain name is an extremely valuable asset. A website with good SEO and using a good domain name becomes even more valuable, and transferrable. So, the domain name and website should become part of succession planning for a business.
Using a street address in the domain name can place restrictions on the website.
What if the business wants to, or is forced to, relocate to a different address? It would probably be very confusing to clients if the same domain name continued to be used.

Perhaps even more important is the diminished value. Would Dr. Newkidontheblock be interested in acquiring an existing SEO'd website using the domain drjoelonginthetooth.ca or even a street-address domain name that is different from where he plans to practice? Or would he be much more interested in acquiring an existing SEO'd website using a good, transferrable domain name?

A good domain name is not an expense; rather, it is an investment in a valuable, transferrable asset that should appreciate in value (very comparable to real estate).

- Canada Domain - CanadaDomains.ca