About alternatives for pooling, you can do it using stride in Conv layers or using different poolings but I do not think that is good idea to skip a method just because of syntax error!
About the MaxPool and MaxUnpool, something I should mention is that you have to provide the indices to MaxUnpool. When you are using MaxPool in your encoder, it returns a tuple (values, indices) and you have to save those and pass them to your decoder.
I think this post explains the situation very well.
