Dario Franchitti and Scott Dixon gave Ganassi a one-two in the first free practice session at Edmonton.
The leading contenders did not even come out for installation laps until the final quarter of an hour, preferring to let the smaller teams clean the track for them at first.
When the pace increased in the closing stages, it was Penske's Ryan Briscoe who first came through to depose previous benchmarks Justin Wilson (Dreyer & Reinbold) and Mario Moraes (KV), before Dixon, championship leader Will Power (Penske) and finally Franchitti took turns in front in quick succession.
Power finished the morning third behind the Ganassi pair, and ahead of his team-mate Helio Castroneves, while Wilson got back up to fifth in the end.
Paul Tracy made a very strong start to his second weekend back at KV, taking sixth place having been a consistent frontrunner in the second half of the session.
His team-mates EJ Viso and Takuma Sato were ninth and 10th, behind Briscoe and Andretti Autosport's lead runner Ryan Hunter-Reay. Sato was soaked in an early incident when he understeered off-course and through the puddles left from the previous night's rain.
There were two stoppages, the first caused by Milka Duno (Dale Coyne) spinning into the tyres at Turn 10, and the second by Bertrand Baguette spinning his Conquest car through an advertising sign after a rough landing from a chicane kerb.
Pos Driver Team Time Gap 1. Dario Franchitti Ganassi 1m03.0885s 2. Scott Dixon Ganassi 1m03.1726s + 0.0841s 3. Will Power Penske 1m03.1732s + 0.0847s 4. Helio Castroneves Penske 1m03.3504s + 0.2619s 5. Justin Wilson Dreyer & Reinbold 1m03.4923s + 0.4038s 6. Paul Tracy KV 1m03.5054s + 0.4169s 7. Ryan Briscoe Penske 1m03.5801s + 0.4916s 8. Ryan Hunter-Reay Andretti 1m03.8048s + 0.7163s 9. EJ Viso KV 1m03.8252s + 0.7367s 10. Takuma Sato KV 1m03.8858s + 0.7973s 11. Tony Kanaan Andretti 1m03.9549s + 0.8664s 12. Mario Moraes KV 1m03.9808s + 0.8923s 13. Alex Tagliani Fazzt 1m04.0583s + 0.9698s 14. Hideki Mutoh Newman/Haas 1m04.2980s + 1.2095s 15. Mario Romancini Conquest 1m04.3564s + 1.2680s 16. Marco Andretti Andretti 1m04.4140s + 1.3255s 17. Raphael Matos De Ferran Dragon 1m04.4304s + 1.3420s 18. Dan Wheldon Panther 1m04.5164s + 1.4280s 19. Tomas Scheckter Dreyer & Reinbold 1m04.5257s + 1.4372s 20. Alex Lloyd Dale Coyne 1m04.6923s + 1.6038s 21. Danica Patrick Andretti 1m04.7031s + 1.6146s 22. Simona de Silvestro HVM 1m04.7061s + 1.6177s 23. Vitor Meira Foyt 1m04.9767s + 1.8883s 24. Bertrand Baguette Conquest 1m05.3084s + 2.2199s 25. Milka Duno Dale Coyne 1m15.2416s + 12.1532s