Henshaw had a late cameo at outside centre, playing the final seven minutes of the Canada game as the 20-year-old's dream-like season with Connacht and Ireland came to an enjoyable end.
Young flanker O'Donnell's first international start was crowned by a second half try, but the player grabbing most of the headlines was hat-trick hero Fergus McFadden.
The versatile Leinster back crossed the Canadian whitewash after 28, 59 and 80 minutes, thus becoming only the sixth player to score three or more tries in a Test match for Ireland since 2000 - Brian O'Driscoll, Denis Hickie, Mike Mullins, Rob Henderson and Kevin Maggs were the others.
McFadden showed what a natural finisher he is and maintained an inspirationally high work-rate around the pitch, leaving quite an impression on Ireland's interim head coach Les Kiss in the process.
"Fergus is just one of those players you want to have around your team. He is such a great character. What he brings to a team in terms of energy and enthusiasm is sensational," said Kiss, speaking after the 40-14 success.
"If he doesn't get selected he is still the same person. He has an uncanny ability to score tries at international level.
"Last week he shipped an injury in the game and he toughed his way through it. He trained through a bit of injury this week and got a knock in the game again but just keeps powering on. I can't speak highly enough about him and the way he played."
Man-of-the-match McFadden, out-half Ian Madigan, who had a hand in two tries and kicked three conversions, and young captain Peter O'Mahony, whose leadership was crucial during some tricky periods, all played important roles as Ireland went two for two on their summer tour.
"I thought Ian deserved the start after managing a difficult game (in Houston). It was quite seductive and tempting to actually overplay his hand last week but he controlled it and managed it and pushed the game where he needed to.
"Tonight, by pure virtue of the rucks having more flow that gave him that little bit more space, he did some lovely things, some lovely touches. There was some errors there as well but our intent was to play a little bit more attacking rugby."
The Australian added: "I thought he was well supported by the back-three (of Andrew Trimble, Fergus and Felix Jones), they did a really good job in terms of supporting his kicking and other short balls he was playing against a very tight Canadian defence at the start of the game."
The June tour has been a learning curve not just for the players but also the coaching staff - Kiss was joined in Houston and Toronto by incoming head coach Joe Schmidt who had an observational role.
The pair fly home with plenty of food for thought, happy no doubt with the back-to-back wins and a widening selection base as well as the visible improvements from the first Test to the next.
"Without a doubt we found out a little about ourselves as players. From a coaching perspective it was certainly encouraging on a lot of fronts," admitted Kiss.
"Sometimes the perception is you can come and get these tier two nations and run it away easily but they were both tough affairs.
"Tonight i think it was the 54th minute it was 14-12. We had to find something, keep our composure and again fantastic leadership through Peter (O'Mahony).
"It pulled us through to a place where we could have the intent to attack as much as we can. And that ended up getting the tries for us. Six new caps and guys have learnt a lot about themselves. I think it has been a really good tour in that respect."