Welcome
@Lizh! If you used 45 mil liner, you would be hard pressed to find a plant that could pierce your liner. You can grow a variety of types of plants in pots IN your pond, but as you said then you have to conceal the pots. I have also seen people bury pots of larger plants near the pond edge, particularily tropical plants that they may want to take inside for the cold months. More work than I want to undertake, personally!
A good way to learn about plants that grow well around ponds in your area is to try to visit some local ponds - either privately owned or even public ponds will give you a good idea of what kinds of plants will grow well and give you the look you are after. Do you have a good pond store near you with display ponds perhaps? Some of the larger professional pond builders in the US offer pond tours throughout the warmer months so you can see other ponds they have built - a great way to get to see lots of ideas for pond plants. Maybe see if there are any local pond owners groups that you could join, even on Facebook for example, as a chance to see what others are planting locally.
Good luck! If you have questions about particular plants, there are bound to be people here who can give you more information. The various types of gunnera that grow here in my particular climate are shade loving plants that will grow to enormous proportions, given the chance. I would love to have one in my garden - just don't have the room!