What visas do I need for traveling to South East Asia if I'm a Canadian Citizen?

I would be a little worried with the length of stay being greater than 30 days given the arrival/return dates. It is the airlines to watch out here - they may decline boarding based on the fear that you will be denied in Thailand (it is well known most airlines will not allow people to fly to Thailand without visas without a return ticket or proof of leaving the country - and deny boarding unless you purchase a valid return within date).

I would suggest getting a single entry Tourist visa (exemption will do for Vietnam return to Thailand) to make things safer for you. You will need to get Vietnam visas either at home before you leave or in Bangkok as they do not have a walkover visa exemption policy (yet). Laos is no problem, but charge a fee of course.

There is also Myanmar to see if you are interested - easy walkover at Mae Sai for 500baht. Tours (and Taichek market) just over the border (and duty free shop).

You get a 30 day visa when you arrive by plane in Thailand and if you get out and back in by land you get another 15 day visa.

For Laos the visa is 42$ US for canadian and available on arrival at the border (30 days).

Cambodia 25$ US be aware of the scam if you travel via Poipet avoid visa scam.

Vietnam, the fastest and cheapest is to get your visa in Phnom Penh, Cambodia. 60$ for 30 days visa and it takes 1 or 2 days.

You can get visas at the border (on arrival) for all of those countries except Vietnam. (Technically, Vietnam does have an embryonic visa-on-arrival service, but you have to apply for it in advance online and it can only be used if you fly into Hanoi or HCMC, so it's useless for most backpackers.)

That said, getting a Vietnamese visa in Bangkok, Vientiane or Phnom Penh is fairly painless, see eg. these instructions for the embassy in Bangkok. It's good to get it out of the way as soon as you arrive though, since normal processing takes a few days.

No visa needed for Thailand, you'll get an entry permit stamped for free. If you leave once, your permit ends, and your counter starts again at zero when you re-enter. There's a limit of 90 days in Thailand per half year, but you won't even come close to that.

Both Laos and Cambodia issue visas at the border, bring dollars and a stack of passport photos. (No big deal if you don't, they'll take a photo there and charge a buck or two for the privilege.)

Thailand: visa-free for 30 days stay when arriving by air, but only 15 days at ground crossings for most nationalities (as of Oct 2013, 30 days at ground crossings for G7 countries: USA, Japan, France, Germany, Italy, UK and Canada). No restrictions on number of entries. If planning to stay longer, get a tourist visa at a Thai consulate (at home or in Vientiane, Laos). Tourist visas allow 60 days stay, extensible by 30 days.

Vietnam: visa-on-arrival available online (if arriving by air). You must get an authorization online a few days in advance. Many services available, I used cheapvietnamvisa.net and it worked ($8 visa + $45 stamping fee at the airport). For ground crossings, you must get the visa at an embassy.

Myanmar: visa required (from the embassy in Bangkok or your home country). If you only intend to go to border towns (e.g. Myawaddi, Tachilek) for a day, usually a visa is not required, you can just leave your passport at the border (and pay $10-$15).

Laos: 30-day single-entry visa-on-arrival available at most crossings, ~$40.

Cambodia: 30-day online e-visa ($28, quick processing) is convenient to avoid hassle/touts, but there's also the visa-on-arrival at border crossings ($20 official price, but they often try to charge more on various pretexts).

Singapore/Malaysia: visa-free for up to 30 days (I think, depends on nationality).

Info updated in Feb 2014... do watch out for changes.

I used to live in Singapore and travel all of these countries (except Laos) extensively.

You can go into and out of Thailand multiple times - each time getting a 30 day visa with no problems.

Getting a Cambodia e-visa online is a breeze and worked well for us when we entered the country by bus at the Vietnam/Cambodian border between Ho Chi Minh City and Phnom Phen.

For Vietnam, we used an online service called myvietnamvisa.com which we thought looked a little sketchy at first but everything checked out when we found reviews online. Basically they will email you a letter which you print off and bring with you. We flew into Ho Chi Minh City and there is a window before immigration labeled 'visa on arrival'. You hand them your letter and your passport and they put a Vietnam visa in your passport which allows you to then go through customs. Works pretty well.

I never traveled to Laos but it looks like you can get a visa on arrival.

If you have time, I would highly recommend visiting Burma (Myanmmar). For this you will have to visit the Burmese Embassy in Bangkok and it will take a couple days.

Also, travel to Malaysia or Philippines requires no visa and visa-on-arrival is easily available in Indonesia.