Marinade then cook or cook then marinade?
If your issue is with the meat being too tough and dry, then your best bet is to marinate beforehand. Marination is the process of soaking food in seasoning before hand to flavor meat and also to cause the marinade to break down some of the tissues in the meat. This will cause more moisture to be absorbed into the end result. This will likely solve your too dry issues rather than cure your meat and dry it out.

If you "marinate" it afterwards, it will likely only flavor the meat but not have the secondary effect of making the meat more moist. The proteins in the meat have already denatured so the marinade will not be able to break down the tissues that it would in a raw product.

If you want to sous vide the meat, I would suggest a lower temperature. 170 degree F is beyond the well done temperature. If you are cooking your pork sous vide at 170 degree F, then the pork will reach a internal temperature of 170 which will result in dry tough meat. Try between 150-160 degree F.

Also traditionally it is marinated before hand rather than afterward.