Scotland manager Gordon Strachan claimed their 1-1 draw against Canada was "invaluable" for his team selection ahead of Sunday's crucial game against Slovenia. Falkirk midfielder Fraser Aird capitalised on some slack defending in the 11th minute to open the scoring for the under-strength visitors, who are ranked 117th in the world.Both sides had half-chances before Steven Naismith diverted home an equaliser 10 minutes before the break.Scotland struggled to create clear chances on a very sticky Easter Road pitch after the break and many of the fans in the crowd - which had an official attendance of 9,158 - booed the hosts off.But Strachan, who handed starts to the likes of Ikechi Anya, Chris Martin and Oliver Burke after a lack of game time for their clubs, felt the performance made things clearer ahead of the World Cup qualifier against a side four points ahead of them in Group F."It was one of our better decisions to have a game," Strachan said. "It has cleared up a lot of things, it has helped a lot of players, but it has helped the coaching staff in particular to where we are going on Sunday. We learned quite a few things."It's not been a great night, it won't be memorable in anyone's minds at the end of careers but it was invaluable to me to use the information we collected for Sunday."Strachan rested Celtic players Scott Brown, Stuart Armstrong, James Forrest and Kieran Tierney following their win over Dundee on Sunday and several of them look likely to come in.The Scotland boss said: "A lot of players found it hard. To use a golf analogy, it's very hard to take two months off and then go and play the Masters, it's not the easiest course in the world. That wasn't the easiest pitch in the world to play on with the conditions and to try and find your form in an international match on a night like this was hard."You could see we were rusty for the first 10-15 minutes and that spooked us for a bit"We could have been braver with passes through people and braver in receiving passes but when you have not played a lot of games it's very hard to just switch on and do that."Strachan admitted there would need to be a major improvement for Sunday's game."It will need to be better unless we're very lucky," he said. "I'm sure a lot of players would have liked to have played a bit better, but that's the way it is and we have to deal with that and use that information."It's very hard to play at international level when you're not firing on all cylinders in your club game but we needed to find that out."Meanwhile, Strachan revealed Bournemouth winger Ryan Fraser was very doubtful for Sunday after missing the friendly with a knee injury."He was excellent in training and we were looking forward to seeing him playing but his knee swelled up," Strachan said. "We will make sure he is all right for his club."