If you believe in Allah, angels, Quran, the messengers and the day of judgement, you perform your prayers, give zakat etc then you are a Muslim Sunni. Sunni belief is based on the following verses:
The Messenger has believed in what was revealed to him from his Lord, and [so have] the believers. All of them have believed in Allah and His angels and His books and His messengers, [saying], "We make no distinction between any of His messengers." And they say, "We hear and we obey. [We seek] Your forgiveness, our Lord, and to You is the [final] destination." (Surah Baqarah Verse 285).
O you who have believed, believe in Allah and His Messenger and the Book that He sent down upon His Messenger and the Scripture which He sent down before. And whoever disbelieves in Allah, His angels, His books, His messengers, and the Last Day has certainly gone far astray. (Surah Nisa Verse 136)
Notice in the verse above there is no mention of Imamah or Imams that our Shia brothers believe in and that is what differentiates the two sides. If Imamah was from the foundations of religion why didn't Allah mention it like he mentioned the other beliefs? He mentioned belief in him, angels, messengers, books, the last day but not Imams?