Is a COM-Domain enough to secure a trademark?

The information you are given is incorrect. In the US you must be using the mark in commerce in order to get even common law trademark protection. You can also file for a state or federal registration-- for a federal registration you need use of the mark in interstate commerce (for a state registration you just need use within that state). You are in Canada so the use rules may be slightly different but I doubt excessively so. Canada also has common law rights in unregistered marks as well as the ability to file for a registration. There is more information here about trademarks in Canada: http://www.ic.gc.ca/eic/site/cipointernet-internetopic.nsf/eng/h_wr02360.html

From a business perspective it's always a good idea to secure the website for your brand as quickly as possible! But just a mere landing page is not enough to show use in commerce, you must be actively selling your goods and/or services (either on the page or elsewhere) in order to have the website count as use in commerce.

This is a very good question, one that most entrepreneurs will want to know. I write to you from the USA, speaking strictly about USA trademark law. A trademark right is only acquired through use of the mark in connection with your good or service in commerce (interstate, if nationally seeking protection). Generally, domain names / website are something a trademark owner or potential trademark user will seek to use to offer a good or service, therefore domain names help prove that you are using a trademark "in commerce" by offering that good/ service online for sale. Once you have a domain, at least in the USA, you have prior rights to use this domain name over someone else who comes later to market with regard to that exact domain name. There are cybersquatting rules to prevent people from offering to sell or ransoming domain names that are close to or exactly the same as a particular brand owner. This has varying levels of complexity, but you can learn more by just Googling "domain name disputes" or "anti-cybersquatting laws."

Usually, prior to seeking to use a given trademark, an entrepreneur will check to see if the desired domain name for the intended trademark is available, because this will be a good indication that someone else is not already using the trademark in commerce. In short, getting a domain name will give you a source of proof that you are using a mark, or intend on using a mark, but it does not technically give you trademark rights per se unless you use that domain to sell or offer to sell your goods or services.

I would recommend, of course after seeking a qualified counsel for assessing the viability/ feasibility of a given trademark, filing an Intent to Use application with the USPTO, only about $400 USD prior to launching any brand, and if you are already using a brand then file a straight forward trademark application with the USPTO (maybe $725 or less). You can check yourself to see if the trademark you want to use/ are already using is currently being used by someone with alleged trademark rights by visiting www.uspto.gov. Click on trademarks search, and try a search of your brand name. If it comes up, then you may want to thing about going a different direction with your name. Talk with an attorney though because not all filed trademarks are valid or are being used, so you'll need better counsel at that point. I hope this helps, good luck, feel free to write me back, happy to help.