Giant common Sunflower, Wild Sunflower (Helianthus gianteus).
It is a perennial herbaceous plant growing up to 4 m tall. The leaves are slender, lanceolate. The flower heads are bright yellow, up to 7 cm diameter. There are many flowers per plant. They are most commonly found in valleys with wet meadows or swamps in the USA and southeast Canada.
If you want more information about this flower, just search the plant's Latin (botanical) name on Google: