When I had a mortgage I used coast capital variable rate product, not sure if it's still the case but the rate was variable but the payment remained locked in for the term. Now yes if rates rise, more of your payment goes to interest leaving a bigger payment when you refinance in 2-5 years but the good news is at that point if you can't afford the payment you can renew the payment back to a 25 year amortization assuming you have over 20% equity they'll happily do this again bringing down your monthly payment, albeit you'll take longer to pay off your loan in this worst case scenario.
I used this strategy when I had my first kid. My wife was off work so a big hit to income I refinanced my mortgage back out over 25 years and brought my payment from $1550 down to $1200/month which helped our cash flow situation.