The Gills raced into a two goal lead after 25 minutes through Barry Fuller and Tom Eaves but were pegged back after the break following goals from John Marquis and Mallik Wilks who bagged in the 67th minute.
A manic end to the game ensured and Gillingham restored their advantage in the 88th minute through Max Ehmer but it was Rovers who had the final say as Paul Taylor earned the home side a point in injury-time.
McCann said afterwards: "It was a great strike from them to go ahead, but to get it back from two down we’ve shown a lot of character.
"That’ll have to go down as one of the most one-sided 3-3 draws you’ll see, we’ll always see a draw as points dropped at home no matter who you play.
"We’ve had 32 shots on goal compared to their three, but to come from behind twice shows that we have that belief to get something out of games.
"We gave ourselves a mountain to climb, but some of our play today was excellent, we’ll address this game and see where we can improve ahead of Tuesday night.
"The late goal could have killed us, but we’ve got one back through a great bit of play from Paul Taylor, and we could’ve then won it in the last minute.
"I’ve said it before that this is a tremendous group to work with, I’ve been very impressed with what they’ve done here, but we’re still learning and always improving."