Kirwan will be watching both teams closely with qualification for the quarter-finals at stake in the evenly balanced Pool D.
And though Wales will start as favourites, he believes fellow Kiwi Steve Hansen must beware the unpredictability of the Canadians.
"From a coach's point of view Canada are a scary team because you don't know what to expect," said Kirwan.
"They are a bit unknown on the day, which is uncomfortable for a coach as you want to be in control of as much as you can.
"It is a very open group and though Wales may start favourites ahead of us (Italy), Canada and Tonga, you just never know what might happen."
Indeed while Kirwan was warning Wales, Italy first opponents New Zealand would be best advised to buckle up after Italian coach Kirwan urged his underdogs to play rugby with same passion as they drive.
Kirwan, a World Cup winner in 1987 with the All Blacks, is looking to tap into the psyche of his adopted nation ahead of their opening game of the tournament this Saturday.
And he reckons the car-loving Italians must take the same attitude on the field as they do to the streets of Rome if they are to establish their own identity.
"We don't want to play like New Zealand or France, we want to play like Italy with the same enthusiasm, passion and emotion as they do when they drive," said Kirwan.
"We need to find our style of playing that incorporates everything that makes Italy special, especially their unpredictability.
"If we can play with structure and discipline we could be tough to break down but we must also lay with enough flair and desire to be constructive in attack.
"It is an honour to play at the World Cup and I will tell every player to go out and play the game that they will remember for the rest of their lives. So we will play the house down on Saturday."
Italy have clearly prioritised the game against Wales as their best chance of winning a place in the quarter-finals for the first time though also face a demanding schedule of laying all four pool games in the space of 18 days.
"This scandal would not happen in a tournament in Europe," blasted Italy team manager Marco Bollesam.
"I could not believe it when I saw the draw and the timetable of games as, from our point of view, it is not fair and seriously stops development and recovery.
"But there isn't anything we can do and we just hope the enthusiasm of the players will get us through.Kirwan has named an under-strength side to play the All Blacks though
insisted that naming a complete second-string team would have been wrong
for the World Cup and for rugby despite the temptation to save players
from possible injury.
Trevino second-row Carlo Checchinato, playing in his fourth World Cup, will
captain his country for the first time.
Italy (v New Zealand; Saturday, October 11; Melbourne) G Peens; M
Bergamasco, A Masi, M Barbini, N Mazzucato; F Mazzariol, M Mazzantini; S
Perugini, C Festuccia, R Martinez, C Checchinato (capt), C Bezzi, S Palmer,
M Phillips, M Bergamasco. Replacements: F Ongaro, M Castrogiovanni, S
Parisse, A Benati, A Troncon, R Wakarua-Noema, G Canale.