In recent years the presence of displays has become ubiquitous. They range from small-sized screens, such as smartphones or tablets to large screens as they are found in projection screens or public displays. Each display requires a unique modality of interaction, such as a dedicated input device, direct touch or does not provide any interaction at all. With the ubiquity of smartphones people carry with them a high-end interaction device that can connect to any web-connected screen. To allow quick access, we built uCanvas (“Ubiquitous Canvas”), a system to engage with interactive surfaces. In contrast to previous work no additional hardware is required, nor do users need to install any proprietary software. Our system runs on all current smartphones equipped with magnetometer and accelerometer, which is used to define a canvas and transmit cursor positions to a server connected to the display. To integrate interactive surfaces into applications, we created a lean Javascript library that allows publishers to specify interaction parameters (such as pointing, clicking, menu selection and text entry) by adding just a few lines of code. We built two example applications to evaluate the feasibility of the system and findings show that (1) interaction is intuitive and (2) easy to set up on the user side.