Sienna "Maneater" Miller

Sienna Miller has a new trend -- she's hot for her leading men.

While she was filming "Factory Girl" last month, she was rumored to be hooking up with "Factory" leading man, Hayden Christensen.

And now this month she's filming a new movie, so you know what that means ... new man!

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Sources tell TMZ that Miller is on to her next leading man, James Franco. The two are currently filming "Camille," a movie about two honeymooners' road trip to Niagara Falls. The pair were spotted this weekend in Toronto getting cozy after-hours.

During filming Friday afternoon, the leading pair had to roll around the hay kissing as Franco's shirt was off. Once the set wrapped, sources say the couple took the on-set frolicking off-set, well into the evening. The two took in a concert and were seen canoodling and dancing in the streets together. Around midnight, Miller and Franco got some Chinese food, enjoyed a cigarette together and hit the nightclubs.

The romance continued Saturday when the two were spotted taking in a matinee of "Pirates of the Caribbean: Dead Man's Chest." Franco was seen in the movie caressing Miller's face. After the movie, the pair hit a bookstore called Indigo.