* Altice to pay 350 mln euros a year for three seasons-sources
* Amount represents a doubling of Champions League rights price
* Deal is a blow for Vivendi's Canal Plus and beIN Sports (Adds Altice confirmation, CEO comments, analyst quote, shares reaction)
By Gwénaëlle Barzic and Mathieu Rosemain
PARIS, May 11 (Reuters) - Altice has beaten Vivendi's pay-TV business Canal Plus and Qatari-controlled beIN Sports channels to the rights to broadcast European Champions League soccer matches until 2021 in France.
Altice's French unit SFR Group agreed to pay 350 million euros ($381 million) per year for the rights to three seasons starting in 2018, two sources close to the matter told Reuters on Thursday. SFR is also getting the rights in France for the Europa League soccer tournament, which ranks below the main Champions League.
Vivendi shares were trading down 2.3 percent at 1215 GMT while Altice and SFR shares were up 1.5 percent and 1.8 percent respectively.
The loss of the rights for Europe's biggest soccer competition puts further pressure on Canal Plus in France, which has lost many customers in the face of new competition from Netflix and beIN Sports.
It also represents a blow for beIN Sports, which gained many customers via its coverage of the Champions League.
Altice confirmed on Thursday that it acquired the exclusive broadcasting rights for the Champions League in France and non-exclusive French-language rights in Luxembourg, Switzerland and Monaco.
The price is double the combined sum Canal Plus and beIN Sports paid for the 2015-2018 period, when the two companies shared the Champions League TV rights, and highlights the growing appetite of deep-pocketed telecom companies for exclusive TV content.
In Britain, BT has beaten arch-rival Sky to retain the rights to broadcast Champions League soccer matches until 2021, agreeing to pay 1.2 billion pounds -- nearly a third more than last time.
In France, Altice has said repeatedly it was ready to invest heavily in its content offering to lure more customers to its broadband and TV bundles.
"This move underlines Altice's ambition to continue to invest in the most powerful programs that bring together the largest audiences," Chief Executive Michel Combes said in a statement.
SFR also bought French broadcast rights for English Premier League soccer for the three seasons starting in 2016, paying more than 300 million euros.
Such investments are weighing on SFR's profitability and it remains difficult to evaluate their impact on customers' choices.
"This is a good marketing stunt," said Thomas Coudry, an analyst at Bryan, Garnier & Co. "On the other hand, in terms of profitability, it's less obvious," he said.
SFR may have to either significantly expand its customer base or increase subscription prices to make a profit out of the newly-acquired TV rights, said Coudry, who has a "buy" rating on Altice and "neutral" on SFR. ($1 = 0.9188 euros) (Editing by Jean-Michel Belot and Tom Pfeiffer)