In month of April you will not access of Manali Leh Highway via Rohtang La Pass. As it is fully covered in snow. There is no chance to do Leh Ladakh in April from Manali Side. Try from Srinagar - Chandigarh - side. But Manali Leh is much fun.
Hey Navneet, Leh & Ladakh is really good in April Tripoto offers some good options. Attcahed below with my comments are some packages. Please take a look, fill the form and someone will get in touch with you. Thanks!