Ryan Reynolds seen leaving Sandra Bullock’s house on his motorcycle

Could they? Would they? Have they? That's what many are wondering about Ryan Reynolds and Sandra Bullock after he was seen leaving her Los Angeles house this past weekend on his motorcycle.

True, it's no shocker the two BFFs spend time with each other. The two have vacationed together . . . as couples, back when Reynolds was married to Scarlett Johansson and Bullock was with Jesse James. But the Canadian hottie was also spotted hiking with Bullock earlier this month in Jackson Hole, Wyoming, where Bullock's father lives. Hmmm . . .

It's been said the secret to a successful relationship is maintaining a good friendship. The two have always been chummy.

The two longtime friends first met in 2000 when Reynolds was just a sitcom actor on "Two Guys, a Girl and a Pizza Place." But it was their 2009 mega hit "The Proposal" that solidified their friendship.

Doesn't hurt the movie was a big money maker - the rom-com took in more than $314 million (US) at the box office. And they have fun together, too, as evidenced by this Funny or Die video they made with their "Proposal" costar Betty White. (Warning: NSFW language.)

"[Sandra is] a catalog of old hip-hop tunes — it's incredible," Ryan Reynolds told People Magazine back in June 2009. "And she looks terrific naked."

(He was referring to the much-talked about comedic scene where the two end up naked on the floor — but still!)

Asked about the sparks between them on screen, Reynolds said: "This kind of chemistry and fireworks ... there's nothing you can do to manufacture it, or edit it together. It's just there or it's not. And to have that every day was literally like driving a Ferrari around on set."

The two have a lot in common off-screen as well. Bullock's dad worked for the United States Army, while Reynold's papawas a RCMP officer. They both dropped out of college, although Sandy eventually got her credits to receive her degree. Like Reynolds to Alanis Morrisette, Bullock was engaged to actor Tate Donovan for a long while (before eventually calling things off). They have both been recognized by People Magazine; he as Sexiest Man Alive in 2010, and she as Woman of the Year that same year.

Both are recently single and have reportedly nursed their failed marriage wounds together. Bullock's divorced from Jesse James was finalized in June 2010, and Reynolds' from Johansson in July 2011.

But, back to their chemistry! They were nominated for MTV Movie Awards Best Kiss, Teen Choice Award for Choice Movie: Liplock, and People's Choice for Favourite On Screen Team for The Proposal.

Even if they're keeping the relationship purely platonic, Reynolds and Bullock will be seeing a lot of each other for the foreseeable future. TV Guide reports that they will work together on an animated comedy called "And Then There Was Gordon" for Reynolds' new TV company DarkFire. They are also working together on a new movie, "Most Wanted."