CA is generally seen as more prestigious and the big 4 firms typically take only candidates with CA's...however, having said that a CPA is still a good qualification to have, certainly better than having nothing..the difference between the two comes down to the prerequisites required and the knowledge/skills needed to achieve the qualification..but it would probably be best to research the two to find out the exact differences
..i have no idea if you can receive both- but the answer is, whilst probably possible there would be little merit in having both (ie, it wouldnt improve job prospects or anything), becuase they are so similar