Cambodia is the ideal country l if you want a sporting holiday, because there is something to do all year round! You should note, though, that the months of April, May and June are the least pleasant, because of the intense heat. You can walk, trek and cycle all over Cambodia. If you like water sports then snorkelling and diving are very good on the south coast, and you can kayak on lots of the rivers and even on Tonlé Sap lake.
Even in the rainy season the scenery is magnificent because it is very green, and a little tropical rain from time to time refreshes the air!
Tonlé Sap changes a lot over the year: in the dry season, you can easily visit a floating village and see the bamboo constructions "behind the scenes" which hold up the houses on their stilts! After the rainy season, the water covers these constructions and you have to visit floating villages by boat.
So the floating villages can be visited all year round but the always magnificent scenery varies.
But a lot of the cruises from Siem Reap to Battambang or to Phnom Penh are not available during the dry season because the water level is too low.