We ended up just a little over our budget in Vietnam. As with Thailand, we budgeted $50 a day for the pair of us, and we ended up spending $55.42 per day. So a little over but not drastically so. Given that we had $100 budgeted for travel from Cambodia, and that we were under budget in Cambodia, things will probably work out fairly well for Asia as a whole.
So that's $1496.40 over 27 days, with most going to food and then accomodation as you can see in the screenshots below.
As with Thailand and Cambodia, cash is king here, and we used it almost everywhere. The Vietnamese Dong is under fairly heavy inflation, and is currently worth somewhere around 18 500 dong to CAD$1. It's a bit odd at first to be paying with 500 000 Dong notes, but you eventually get used to the large numbers everywhere. Due to the inflation and changing Dong values, some places list their prices in US$ but charge in Dong at the current rates. Especially when negotiating prices, be careful with the exchange rate they use - there's no point negoting hard on a price in US$ if they then just add 20% to the exchange rate they quote you.
We didn't have too much trouble with ATMs here. Many ATMs have a fairly low withdrawal limit of 2 million Dong ($100), but we found Citibank in HCMC and Hanoi let you take up to 8 million with fees of only $3. There's quite a lot of options for banks, but it seemed they all charge fees these days - some publisized and others you only find out after confirming the transaction.