VIVENDI'S Canal Plus has offered to buy all the shares it does not own in South Africa's MultiChoice Group for roughly $1.7 billion to strengthen its hand in a competitive international pay TV market. Canal Plus, the top shareholder in MultiChoice with a 31.67% stake according to LSEG data, said it would likely pay 105 rand in cash per share, a 40% premium to MultiChoice's closing share price on Wednesday. Shares in MultiChoice surged in Thursday trade but remained below the offer price. They were last up 24.83% at 93 rand. Canal Plus said its offer, worth 31.7 billion rand according to…