MONTREAL, Canada - Briton Paul Di Resta topped the times for Force India in a British one-two at the end of Friday's rain-hit opening free practice session for this weekend's Canadian Grand Prix.In a difficult session during which there was a brief late spell of drying conditions, Di Resta wound up fastest ahead of fellow-Briton Jenson Button of McLaren.SPECIAL MOMENTFor Di Resta and his team, it was a perfect way to mark the first morning of the Force India's 100th Grand Prix.Frenchman Romain Grosjean, who crashed in every session in Monaco, was third fastest for Lotus ahead of two-time World champion Fernando Alonso of Ferrari and Kimi Raikkonen, the 2007 champion, in the second Lotus.On an unpredictable morning, Australian Daniel Ricciardo was seventh for Toro Rosso ahead of German Nico Rosberg, who dominated every session for Mercedes in Monaco two weeks ago, and controversial Mexican Sergio Perez, in the second McLaren.Defending triple World champion German Sebastian Vettel was ninth ahead of his Red Bull team mate Australian Mark Webber with Brazilian Felipe Massa in the second Ferrari taking 11th place.Briton Lewis Hamilton, seeking his fourth win at the Circuit Gilles Villeneuve, was down in 16th in the second Mercedes.SOME ACTIONVenezuelan Pastor Maldonado delivered the only major accident in the session when he smashed into the wall in the final minutes and damaged the front wing of his Williams car.Di Resta said he was uncertain what his fastest time meant for the weekend ahead because of the variable weather conditions.He said: "There were yellow flags in sector one, but I was very cautious through it. I'm not so sure what it all comes down to - we had a good run on the inters."In the dry, the car doesn't seem too bad. FP2 is going to be busy as we've got lot of tyre work to do given the forecast, but I'm looking forward to it."This is the worst GP of the year for weather, it's so unpredictable and we spend more time hiding from the rain here than anywhere else. I think anything in the top six on Sunday will be exceptional."Button, World champion in 2009, was happy to see the rain which he believes is his best hope of producing a repeat of his famous rain-splattered victory of 2011."In Monaco, the outright result wasn't great, but in terms of our improvement in performance it was relatively good," Button said."We have got some new parts on the car here to test, which is exciting, and hopefully they will give us what we expect. It still doesn't mean that we will be fighting for a win in dry conditions."If it is mixed, we have got to be ready for every scenario and I think that we can do well in that situation."Free Practice Session from the F1 Canadian Grand Prix1. Paul Di Resta (Britain) Force India - Mercedes 1:21.020 2. Jenson Button (Britain) McLaren 1:21.108 3. Romain Grosjean (France) Lotus - Renault 1:21.258 4. Fernando Alonso (Spain) Ferrari 1:21.308 5. Kimi Raikkonen (Finland) Lotus - Renault 1:21.608 6. Daniel Ricciardo (Australia) Toro Rosso - Ferrari 1:22.068 7. Nico Rosberg (Germany) Mercedes 1:22.402 8. Sergio Perez (Mexico) McLaren 1:22.587 9. Sebastian Vettel (Germany) RedBull - Renault 1:23.047 10. Mark Webber (Australia) RedBull - Renault 1:23.131 11. Felipe Massa (Brazil) Ferrari 1:23.341 12. Valtteri Bottas (Finland) Williams - Renault 1:23.352 13. Jean-Eric Vergne (France) Toro Rosso - Ferrari 1:23.386 14. Adrian Sutil (Germany) Force India - Mercedes 1:23.417 15. Esteban Gutierrez (Mexico) Sauber - Ferrari 1:23.957 16. Lewis Hamilton (Britain) Mercedes 1:25.054 17. Nico Huelkenberg (Germany) Sauber - Ferrari 1:25.354 18. Giedo van der Garde (Netherlands) Caterham - Renault 1:25.753 19. Max Chilton (Britain) Marussia - Cosworth 1:25.821 20. Alexander Rossi (U.S.) Caterham - Renault 1:27.143 21. Pastor Maldonado (Venezuela) Williams - Renault 1:27.522 22. Jules Bianchi (France) Marussia - Cosworth 1:29.306 Stay with Wheels24 for the 2013 Canadian GP weekend.