Tours within 8 hours from Paris and London's airports.?

My dad, sistah, and I are travelin’ to Canada from Saudi Arabia, Riyadh and on our way there we’re gonna stop either in Paris or London. Is there any buses to take us from either’s airports to tours while the 8 to 12 hours of waitin’ in the airport? On the way to Canada we will stop, and on the way back to Riyadh we will stop, too. Once in London and once in Paris. Please, gimme a site where I can find the prices and where I can book a ride in the bus for tours. Thanks in advance for your reply.

Love,

Sara a.k.a. Sasha a.k.a. Bunny Boo

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