First of all in nutshell, leaving out many tangents this whole tale has; here's the origins of Osiris;
Already, it seems like a big stretch to compare this to the Christ Resurrection.The original form of the myth states that Osiris was killed by a wooden sarcophagus secretly being made to his measurements by Seth, who was jealous of Osiris's position as king, and so plotted to kill him and take his place. A party had been held where the coffin was offered to whoever could fit inside. A few people tried to fit in, but to no avail. Osiris was encouraged to try, but as soon as he lay back, the lid slammed on him and was locked. It was then sealed with lead and thrown into the Nile. Upon hearing that Osiris was gone, Isis set out to look for him. She was afraid that without proper ceremonies and burial Osiris would not be able to go to the place of the dead. She later learned that the coffin had floated down the Nile river up to the coast of Byblos (now in modern day Lebanon) and became embedded in the trunk of a cedar tree. She also learned that the cedar tree had been taken and used as a pillar to support a palace for the king of Byblos. When traveling back, along the Nile River, she left the coffin in an area of marshland. Set, while hunting, finds Osiris' coffin and dismembered him into 14 parts, scattering them across the land of Egypt. Each part represented one of the 14 full moons (each year has 12 to 14 full moons).[1]
Once again Isis set out to look for the pieces and she was able to find 13 of the 14 parts, with the help of Nephthys, Set's sister-wife, but was unable to find the 14th, as it had been eaten by a fish. Instead, she fashioned a phallus out of gold and sang a song around Osiris until he came back to life.
Osiris was resurrected. He could have proper ceremonies and burial. [Other legends say, he only had enough life put into him impregnate Isis with their son Horus]
Due to this experience, Osiris became Lord of the Dead, and the Afterlife. [2].
From Wiki;
David J. MacLeod argues that the resurrection of Osiris differs from Jesus Christ, saying:
Perhaps the only pagan god for whom there is a resurrection is the Egyptian Osiris. Close examination of this story shows that it is very different from Christ's resurrection. Osiris did not rise; he ruled in the abode of the dead. As biblical scholar, Roland de Vaux, wrote, 'What is meant of Osiris being "raised to life?" Simply that, thanks to the ministrations of Isis, he is able to lead a life beyond the tomb which is an almost perfect replica of earthly existence. But he will never again come among the living and will reign only over the dead. This revived god is in reality a "mummy" god.'... No, the mummified Osiris is hardly an inspiration for the resurrected Christ... As Yamauchi observes, 'Ordinary men aspired to identification with Osiris as one who had triumphed over death. But it is a mistake to equate the Egyptian view of the afterlife with the biblical doctrine of resurrection. To achieve immortality the Egyptian had to meet three conditions: First, his body had to be preserved by mummification. Second, nourishment is provided by the actual offering of daily bread and beer. Third, magical spells were interred with him. His body did not rise from the dead; rather elements of his personality - his Ba and Ka - continued to hover over his body.*'[27]

My monitor is color challenged, but the above image should be correct. All the descriptions of Osiris say he was green-skinned and wore mummy bandages, because he was a dead corpse. Not resurrected to life, but magically animated if you will, and it took far longer than three days. Further legends also say, he as well as any other being having once entered the afterworld, could not leave it. The Egyptians believed that dead was dead, even for the gods.
Often what's left out of many tellings of this Myth of Osiris and Isis is: what Isis brought fourth was just a part of Osris' soul: his Ba;
Without all eight pieces of your soul and bodily parts, according to the Egyptians, you were not alive.From Wiki
The Ancient Egyptians believed that a human soul was made up of five parts: the Ren, the Ba, the Ka, the Sheut, and the Ib. In addition to these components of the soul there was the human body (called the ha, occasionally a plural haw, meaning approximately sum of bodily parts). The other souls were aakhu, khaibut, and khat.
...
In the Coffin Texts one form of the Ba that comes into existence after death is corporeal, eating, drinking and copulating.
Isis only revived a piece of Osiris' essence in order to conceive her child. The Ba was thought to look like this;

Furthermore, it was said Isis taught this ability to mummify, and preserve your body for it's trip to the underworld to all Egyptians. It became a central part of their religion and culture, to tend to the needs of their 'souls'. So, this wasn't considered a divine ability, or miracle. Everyone had(has) a Ba.
The ba of Queen Nefertari,
