Seeking suggestions for tree / grass / plants for deck

We have an office in Vancouver, BC, in the west Broadway area. We have a deck outside our office on the 4th floor. It faces north. There are some unknown dead trees in four cedar planters close to the perimeter of the deck that need to be replaced. These planters are about 2ft by 2ft by 2ft. There is direct sunlight most of the day for three of the planters. The fourth planter is in the shade. We need some replacement plants that are not demanding as we can't spend a lot of time maintaining them. We thought maybe Japanese maple or a tall grass. We wonder if anyone has other suggestions, or suggestions on the variety of these plants to use. Would it be ok to plant some annuals or perennials in the same pot as the Japanese maple or is it too much? Thanks.