Gambling is haram, so the question is: Is this gambling? Ordinarily, the answer is no.
The key distinction is the lack of entry fee, without which scholars consider it halal:
... if entry into the prize-draw is free and no money is demanded, then that would not constitute gambling, hence permitted.
If a sweepstakes is merely promotional where no purchase is necessary, then it is like a prize or award that the business volunteers to advertise its products and to attract more customers. Such sweepstakes are permissible in Islam.
Islam Q&A say that there is nothing wrong with that provided (a) the price is not raised for the competition and (b) the purchaser does not buy the product solely for the sake of entering the competition.