What are possible substitutes for pineapple in sweet and sour pork/chicken?
The recipe title kind of answers the question--it is the sweet, and some of the sour.  Pineapple also has a good firmness.  Note that all of the below is speculation, as this is a most unusual substitution request, so I haven't tried any of this.

Fruit will best serve the role of both tart and sour, so almost every reasonable substitute is going to be fruit.

You have indicated you don't like the flavor of pineapple, which for your goal, is probably good as nothing else will provide that distinctive flavor.  While my first choice would be to not make this recipe, where you don't enjoy one of the signature ingredients, if you do, then you want something that:


Has a good body and mouth feel the way pineapple does, even after the pureeing called for in the cited recipe
A floral, complex flavor
Something sweet and tart


In the recipe you cite, the pineapple is canned, so you are not losing its enzymatic action, as the enzymes in the pineapple were deactivated by the heat during the canning process.

What comes first to my mind is mango, perhaps with a mixture of lime and orange juice to replace the acidity of the pineapple juice, and maybe a touch of sugar to balance the flavor.  You will have to find the right balance, depending on your particular fruit--you may want extra acidity from lemon juice, even, or perhaps extra sugar.  I would use something that adds complexity like brown sugar or turbadino depending on where you live if it is needed.

If you try this, however, you will be inventing essentially a new dish, and will have to work out how long to cook the mixture.

Another more radical choice would be canned peaches, perhaps using some of their syrup for sweetness, and again, lemon or lime juice mixed with orange juice for the acidity. This will probably be even more divergent, but peaches have a good floral complexity, and with enough lemon juice, you should be able to find the sweet/sour balance.  Of course, this would be far from authentic.