What will happen if Earth becomes the size of Sun

 If Earth becomes the size of the Sun continents would expand, hence preventing over population. Everyone will be able to have their own plot and at affordable price.

Every body of the water will have more area. But Marine life will be drastically affected as shallower water will gain more heat from the sun, menacing sea creatures that need colder water to survive.

Gravity on Earth will be 28 times stronger than usual. It will result in abrupt increase in Gravitational pressure. Hence, all the buildings and bridges would crumble and collapse. The thick trees that were low to the ground would remain standing.

If Earth becomes the size of the Sun, then it may even have more mass. More mass means it will also have a stronger Gravitational pull. Our satellites would also probably crash down to Earth.

We would have been significantly heavier, and probably wouldn't be able to walk anywhere.

The big twist here is that as gravity increases, time would slow down. So you might be able to live longer, but it would probably be a long life spent lying in bed with aches and pains.

The Earth may even turn into a black hole if it's mass increases to 10 times that of the Sun.