Disneyland California Adventure Cars Land soft opening?

First, soft openings are generally not public knowledge. Second, unless you're one of the privileged few, there's no chance of getting in prior to June 15th.

According to Al Lutz over at MiceAge, June 2nd and June 3rd are private preview parties for Imagineers and Pixar employees and their guests. June 4th through June 8th are slated for Cast Member preview parties. June 9th and 10th are Annual Passholder preview parties with a catch: AP holders will be charged "several hundred dollars" which is going to charity in order to attend the event. June 13th the media arrives, June 14th the park is closed and June 15th is the grand opening but later in the morning, around 9:30 rather than regular park opening time.

During the summer, Magic Morning early entry is offered at Disneyland four days a week and at California Adventure the other three. However, on the four days that California Adventure doesn't have Magic Mornings available to the public, they will allow Annual Passholders early entry to take advantage of Carsland and its offerings.