What's a good Protoss unit mix / strategy to bust a large Photon Cannon base defense?

I was in a FFA with 2 other Protoss and a Terran... towards the end there were a ton of static Photon Cannons guarding bases. I was thinking Immortals with a few Sentries for Guardian Shield would be best... but I wonder if there are any other tips or unit ideas for cheaply breaking up a giant cannon farm to attack an enemy Protoss' base in PvP

Solution 1:

Colossi with Extended Thermal Lance have a range of 9, while Photon Cannons only have a range of 7. You can snipe off the defenses without taking any damage.

Solution 2:

The slightly lower tech option is immortals, who do their full 50 damage to buildings while only taking half damage to their shields (20 maxed at 10).

Solution 3:

Expanding a lot and building up a large, upgraded army is really what it comes down to..... making cannons early or even late can but a Protoss pretty far behind.