City Dog, Country Frog by Mo Willems, illustrated by Jon J Muth

From chapters.ca:
In spring, when City Dog runs free in the country for the first time, he spots Country Frog sitting on a rock, waiting for a friend. "You'll do," Frog says, and together they play Country Frog games. In summer, they meet again and play City Dog games. Through the seasons, whenever City Dog visits the country he runs straight for Country Frog's rock. In winter, things change for City Dog and Country Frog. Come spring, friendship blooms again, a little different this time.